Handle .txx/tpp headers.

[sean-mcmanus]

Add .txx/.tpp support from #13808 . The actual fix for the bug in the issue is actually on the cpptools side though.

[bhubavenski]

if you can add also .ipp as for implementation file or better add it as an option to the user to specify in what extension his header files are ending. ( if it's possible )

[sean-mcmanus]

if you can add also .ipp as for implementation file or better add it as an option to the user to specify in what extension his header files are ending. ( if it's possible )

ipp is already handled.