CppTools: Rewrite cppdoxygen.cpp with cplusplus-keywordgen

Braces all over the place since the tool does not respect the coding
style and cppdoxygen.cpp was changed with regard to the braces coding
style in the meantime:

  commit 29a93998
  Remove braces for single lines of conditions

Next step is to use the tool for updating the qdoc/doxygen keywords.

Change-Id: Ib95b5991ebd794d144848ae052fa7f28a6d10850
Reviewed-by: David Schulz <david.schulz@theqtcompany.com>
Reviewed-by: Orgad Shaneh <orgads@gmail.com>