Added --filename-suffix and --filename-ext to flatc (#5778)

* Fixed refractoring issue in reflection/generate_code.sh. Also, mv deletes the original file, so I don't need to clean it up manually in that case.

* Added --filename-suffix and --filename-ext to flatc

* Fixed typo and added example generation of suffix and extension for C++

* Removed extra ;

* Removed clang-format block from a region that didn't need it. Fixed an auto format of another clang-format block

* Added docs, fixed pointer alignment, removed suffix test file