fix: ignore fixer tool configurations that are missing patterns This is to prevent a crash under the same circumstances. This is also to avoid data loss due to accidental application of a fixer tool to all files, if the matching logic somehow changed to that effect. Affecting all files until otherwise configured would be dangerous, and not very useful. We shouldn't abort because there may be other fixers, and it may still be useful to run them without having to adjust configuration. A user might not feel confident in changing configs, for example. Differential Revision: https://phab.mercurial-scm.org/D6693

fix: add a test case around the effect of cwd on pattern matching This was not covered by previous tests. It is related to a regression encountered at Google due to misconfiguration of [fix]. Differential Revision: https://phab.mercurial-scm.org/D6692

fix: remove support for :fileset sub-config in favor of :pattern Differential Revision: https://phab.mercurial-scm.org/D6691