This adds a flag to lit for detecting and updating failing tests when
possible to do so automatically. The flag uses a plugin architecture
where config files can add additional auto-updaters for the types of
tests in the test suite. When a test fails with `--update-tests` enabled
lit passes the test RUN invocation and output to each registered test
updater until one of them signals that it updated the test (or all test
updaters have been run). As such it is the responsibility of the test
updater to only update tests where it is reasonably certain that it will
actually fix the test, or come close to doing so.
Initially adds support for UpdateVerifyTests and UpdateTestChecks. The
flag is currently only implemented for lit's internal shell, so
`--update-tests` implies `LIT_USE_INTERNAL_SHELL=1`.
Builds on work in #97369Fixes#81320
bb8b9ac0ba
