cppcheckdata: Use instance attributes in Cppcheckdata (#3029)

This commit makes CppcheckData class to use instance attributes instead
of class attributes.

Since class attributes are mutable (list), when you append to them, they
don't promote to instance variable which means when you call parsedump()
multiple times data just gets appended to them.

Found by samed on the forum:
https://sourceforge.net/p/cppcheck/discussion/general/thread/c6e1210ec2/

addons/cppcheckdata.py

@@ -852,15 +852,14 @@ class CppcheckData:
     @endcode
     """
 
-    rawTokens = []
-    platform = None
-    suppressions = []
-
     def __init__(self, filename):
         """
         :param filename: Path to Cppcheck dump file
         """
         self.filename = filename
+        self.rawTokens = []
+        self.platform = None
+        self.suppressions = []
 
         files = []  # source files for elements occurred in this configuration
         platform_done = False