Part of https://github.com/flutter/flutter/issues/127135
Part of https://github.com/flutter/flutter/issues/125115

Addresses issues:
- https://github.com/flutter/flutter/issues/127135
- https://github.com/flutter/flutter/issues/99767

Creates a matcher class that we can use for `ProcessResult` to check for the exit code.

*List which issues are fixed by this PR. You must list at least one issue.*

*If you had to change anything in the [flutter/tests] repo, include a link to the migration guide as per the [breaking change policy].*