Fix issue 8899: False positive returnDanglingLifetime when returning by value

This fixes the FP from:

```cpp
#include <string>

class MyString
{
        public:
        MyString(char* source)
        {
                length = strlen( source );
                buffer = new char[length+1];
                if( buffer )
                {
                        strcpy( buffer, source );
                }
        }

        char* buffer;
        int length;
};

MyString Foo()
{
        char arr[20];
        sprintf(arr, "hello world");

        return arr;
}

void main()
{
        MyString str = Foo();

        printf(str.buffer);
}
```

lib/valueflow.cpp

@@ -2743,6 +2743,27 @@ struct Lambda {
     }
 };
 
+static bool isDecayedPointer(const Token *tok, const Settings *settings)
+{
+    if (!tok)
+        return false;
+    if (astIsPointer(tok->astParent()) && !Token::simpleMatch(tok->astParent(), "return"))
+        return true;
+    if (!Token::simpleMatch(tok->astParent(), "return"))
+        return false;
+    if (!tok->scope())
+        return false;
+    if (!tok->scope()->function)
+        return false;
+    if (!tok->scope()->function->retDef)
+        return false;
+    // TODO: Add valuetypes to return types of functions
+    ValueType vt = ValueType::parseDecl(tok->scope()->function->retDef, settings);
+    if (vt.pointer > 0)
+        return true;
+    return false;
+}
+
 static void valueFlowLifetime(TokenList *tokenlist, SymbolDatabase*, ErrorLogger *errorLogger, const Settings *settings)
 {
     for (Token *tok = tokenlist->front(); tok; tok = tok->next()) {
@@ -2846,8 +2867,9 @@ static void valueFlowLifetime(TokenList *tokenlist, SymbolDatabase*, ErrorLogger
             const Variable * var = getLifetimeVariable(tok, errorPath);
             if (!var)
                 continue;
-            if (var->isArray() && !var->isStlType() && !var->isArgument() && tok->astParent() &&
+            if (var->nameToken() == tok)
-                (astIsPointer(tok->astParent()) || Token::Match(tok->astParent(), "%assign%|return"))) {
+                continue;
+            if (var->isArray() && !var->isStlType() && !var->isArgument() && isDecayedPointer(tok, settings)) {
                 errorPath.emplace_back(tok, "Array decayed to pointer here.");
 
                 ValueFlow::Value value;

test/testautovariables.cpp

@@ -717,7 +717,7 @@ private:
               "    return str;\n"
               "}");
         ASSERT_EQUALS(
-            "[test.cpp:3] -> [test.cpp:3] -> [test.cpp:4]: (error) Returning pointer to local variable 'str' that will be invalid when returning.\n",
+            "[test.cpp:4] -> [test.cpp:3] -> [test.cpp:4]: (error) Returning pointer to local variable 'str' that will be invalid when returning.\n",
             errout.str());
 
         check("char *foo()\n" // use ValueFlow
@@ -727,7 +727,7 @@ private:
               "    return p;\n"
               "}");
         ASSERT_EQUALS(
-            "[test.cpp:3] -> [test.cpp:3] -> [test.cpp:5]: (error) Returning pointer to local variable 'str' that will be invalid when returning.\n",
+            "[test.cpp:4] -> [test.cpp:3] -> [test.cpp:5]: (error) Returning pointer to local variable 'str' that will be invalid when returning.\n",
             errout.str());
 
         check("class Fred {\n"
@@ -739,7 +739,7 @@ private:
               "    return str;\n"
               "}");
         ASSERT_EQUALS(
-            "[test.cpp:6] -> [test.cpp:6] -> [test.cpp:7]: (error) Returning pointer to local variable 'str' that will be invalid when returning.\n",
+            "[test.cpp:7] -> [test.cpp:6] -> [test.cpp:7]: (error) Returning pointer to local variable 'str' that will be invalid when returning.\n",
             errout.str());
 
         check("char * format_reg(char *outbuffer_start) {\n"
@@ -795,7 +795,7 @@ private:
               "    return x+5;\n"
               "}");
         ASSERT_EQUALS(
-            "[test.cpp:2] -> [test.cpp:2] -> [test.cpp:3]: (error) Returning pointer to local variable 'x' that will be invalid when returning.\n",
+            "[test.cpp:3] -> [test.cpp:2] -> [test.cpp:3]: (error) Returning pointer to local variable 'x' that will be invalid when returning.\n",
             errout.str());
 
         check("char *foo(int y) {\n"
@@ -803,7 +803,7 @@ private:
               "    return (x+8)-y;\n"
               "}");
         ASSERT_EQUALS(
-            "[test.cpp:2] -> [test.cpp:2] -> [test.cpp:3]: (error) Returning pointer to local variable 'x' that will be invalid when returning.\n",
+            "[test.cpp:3] -> [test.cpp:2] -> [test.cpp:3]: (error) Returning pointer to local variable 'x' that will be invalid when returning.\n",
             errout.str());
     }
 
@@ -813,7 +813,7 @@ private:
               "    return (char *)x;\n"
               "}");
         ASSERT_EQUALS(
-            "[test.cpp:2] -> [test.cpp:2] -> [test.cpp:3]: (error) Returning pointer to local variable 'x' that will be invalid when returning.\n",
+            "[test.cpp:3] -> [test.cpp:2] -> [test.cpp:3]: (error) Returning pointer to local variable 'x' that will be invalid when returning.\n",
             errout.str());
     }
 
@@ -1533,6 +1533,15 @@ private:
               "}\n");
         ASSERT_EQUALS("[test.cpp:2] -> [test.cpp:3] -> [test.cpp:1] -> [test.cpp:3]: (error) Returning lambda that captures local variable 'a' that will be invalid when returning.\n", errout.str());
 
+        check("struct e {};\n"
+              "e * j() {\n"
+              "    e c[20];\n"
+              "    return c;\n"
+              "}\n");
+        ASSERT_EQUALS(
+            "[test.cpp:4] -> [test.cpp:3] -> [test.cpp:4]: (error) Returning pointer to local variable 'c' that will be invalid when returning.\n",
+            errout.str());
+
         check("auto f(std::vector<int>& a) {\n"
               "    auto it = a.begin();\n"
               "    return [=](){ return it; };\n"
@@ -1605,6 +1614,25 @@ private:
               "  }\n"
               "};\n");
         ASSERT_EQUALS("", errout.str());
+
+        check("struct a {\n"
+              "    a(char* b) {}\n"
+              "};\n"
+              "a f() {\n"
+              "    char c[20];\n"
+              "    return c;\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
+
+        check("struct a {\n"
+              "    a(char* b) {}\n"
+              "};\n"
+              "a g() {\n"
+              "    char c[20];\n"
+              "    a d = c;\n"
+              "    return d;\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void danglingLifetimeFunction() {
@@ -1652,7 +1680,7 @@ private:
               "  x[3];\n"
               "}\n");
         ASSERT_EQUALS(
-            "[test.cpp:4] -> [test.cpp:4] -> [test.cpp:7]: (error) Using pointer to local variable 'y' that is out of scope.\n",
+            "[test.cpp:5] -> [test.cpp:4] -> [test.cpp:7]: (error) Using pointer to local variable 'y' that is out of scope.\n",
             errout.str());
 
         check("void foo(int a) {\n"