meson: Clean up ICU dependency search

Since we are using Meson 0.60.0 or later, use CMake to help us find ICU,
which is cleaner and more comprehensive, and allows us to use libicu_dep
= depedency(...) even on Visual Studio, where CMake will find the
appropriate ICU headers and libraries for us internally.

Sadly, due to peculiarities, we have to live with the warning that comes
up as we needed to look for ICU in the older method instead of the
recommended modules: ['ICU::uc'] method.

meson.build

@@ -40,17 +40,9 @@ if ['libidn2', 'auto'].contains(enable_runtime)
 endif
 
 if ['libicu', 'auto'].contains(enable_runtime)
-  libicu_dep = dependency('icu-uc', required : false)
-  if not libicu_dep.found() and cc.has_header('unicode/ustring.h')
-    # MSVC: the debug configuration of ICU generated the libraries with d suffix
-    # we must handle this and search for the right library depending on the
-    # build type. Note debugoptimized is just a release build with .pdb files enabled
-    if cc.get_id() == 'msvc' and buildtype == 'debug'
-      libicu_dep = cc.find_library('icuucd', required : false)
-    else
-      libicu_dep = cc.find_library('icuuc', required : false)
-    endif
-  endif
+  libicu_dep = dependency('icu-uc', 'ICU',
+                          components: 'uc',
+                          required : false)
   if libicu_dep.found()
     if enable_runtime == 'auto'
       enable_runtime = 'libicu'