Port member initialization from constructor to declaration (C++11)

Using `clang-tidy`'s `modernize-use-default-member-init` check and
manual review of the changes, and some extra manual changes that
`clang-tidy` failed to do.

Also went manually through all of `core` to find occurrences that
`clang-tidy` couldn't handle, especially all initializations done
in a constructor without using initializer lists.

modules/gdscript/gdscript_tokenizer.h

@@ -176,7 +176,7 @@ public:
 	virtual bool is_ignoring_warnings() const = 0;
 #endif // DEBUG_ENABLED
 
-	virtual ~GDScriptTokenizer(){};
+	virtual ~GDScriptTokenizer() {}
 };
 
 class GDScriptTokenizerText : public GDScriptTokenizer {