rhg: add support for ignoring all extensions
Some workflows just want what `rhg` does and don't care about any extensions,
this makes it easier.
Differential Revision: https://phab.mercurial-scm.org/D12385
BasedOnStyle: LLVM
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BreakBeforeBraces: Linux
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IncludeCategories:
- Regex: '^<'
Priority: 1
- Regex: '^"'
Priority: 2