Description

Switch tool tests to use build_runner. The test execution should be noticeably faster, with the trade-off of doing compilation up front. The compilation artifacts can be shared across shards though, which should allow us to increase overall test throughput.

Related Issues

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]). This will ensure a smooth and quick review process.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes tests for all changed/updated/fixed behaviors (See Test Coverage).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (flutter analyze --flutter-repo) does not report any problems on my PR.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require Flutter developers to manually update their apps to accommodate your change?

• Yes, this is a breaking change (Please read Handling breaking changes).
• No, this is not a breaking change.