Wizards: Port "Code Snippet" Project Wizard to .json wizard

Code Snippet is the last .xml-based wizard shipped with Qt Creator.
This change ports it to the .json-based wizard format. Instead of
supporting just qmake-based projects (like it did), the new version
supports just CMake-based projects.

Change-Id: Ie64114165fff5d56ddf82041cc4d5f90c44fe77b
Reviewed-by: hjk <hjk@qt.io>

share/qtcreator/templates/wizards/codesnippet/main.cpp

@@ -1 +1 @@
-%CODE%
+%{CodeSnippet}