Update clang-format to version 11

This is taken from the Godot repository, so formatting is similar. This
updates the style rules as well.

Also fix style in files to conform with this version.

include/core/String.hpp

@@ -14,7 +14,6 @@ class PoolStringArray;
 class String;
 
 class CharString {
-
 	friend class String;
 
 	godot_char_string _char_string;