Modernize clang-format plugin
This plugin is very old and still uses the gsetting directly for "format-on-save".
Instead, it should be converted to implement an IdeFormatter.
Additionally, it should look at the target buffer/file and try to locate the closest .clang-format
to the file, by checking the current directory and walking up to the project root. That will improve the situation when opening files in subprojects with their own .clang-format
.