fix: new extension for automatically modifying file contents
This change implements most of the corresponding proposal as discussed at the
4.4 and 4.6 sprints: https://www.mercurial-scm.org/wiki/AutomaticFormattingPlan
This change notably does not include parallel execution of the formatter/fixer
tools. It does allow for implementing that without affecting other areas of the
code.
I believe the test coverage to be good, but this is a hotbed of corner cases.
Differential Revision: https://phab.mercurial-scm.org/D2897
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273ce12ad8f1` will report some style violations on a very old commit).