KDEClangFormat: se the same source file extensions in clang-format script and target
Previously the clang-format.sh git hook script didn't specify the file extensions to format; however it looks like with recent(?) clang-format versions 'git clang-format' will consider .json files if such files were changed by a commit, which makes the script fail, see: !254 (closed)
Sepcify the file extensions by passing --extensions to 'git clang-format' command.
Also add ".hpp" to the file extensions we format, and use the same list of file extensions everywhere.