cmake.lang: Update keywords to 3.18.2 syntax

Mostly adds missing and/or new symbols:

• New built-in commands:
  • add_compile_definitions()
  • cmake_language()
  • target_precompile_headers()
• Now deprecated commands:
  • qt_wrap_cpp()
  • qt_wrap_ui()
• Some new built-in variables + less tolerant regex
• Loads of missing and/or new operators