This is the first in a sequence of PRs which will lint only changed files on presubmit. The process is the following:
1. Add new `bringup: true` builders that lint only changed files. `bringup: true` builders don't run in presubmit, and since after landing this no files will be detected as changed, these builders will not do anything yet.
1. Remove `bringup: true`. This will allow the new builders to run in presubmit.
1. Ask the team to monitor the new checks on PRs to make sure they are doing the right thing.
1. When we're reasonably sure that the checks are doing the right thing, add `presubmit: false` to `mac_clang_tidy` and `linux_clang_tidy` so that we no longer needlessly lint all files in presubmit.
Related https://github.com/flutter/flutter/issues/105068
38d3dcbc72