Bug #3197
Rework usage of gitattributes and filter in source code formatting scripts
Description
The change from uncrustify to clang-format and the related changes to the management of the source code formatting scripts has exposed some fragility of our usage of gitattributes for making sure the correct files are passed through the correct formatting processes.
We need to check if our use of the filter attribute is correct and works in custom scripts or for users that filter files directly.
Split up source code formatting scripts
Split up copyright header checking from uncrustify and updated docs
accordingly.
Refs #3197
Change-Id: I68bade3ff5b7d2fc1cdaeff6a8b4021137af1735