[record_use] Use case: Flutter `IconTreeShaker`

[dcharkes]

We should prototype and implement the Flutter icon tree shaker with package:record_use.

1. Prototype to prove out that that it works.
2. And, then figure out what we need to actually land it.

Sources:

• https://github.com/flutter/flutter/blob/7100df24f611a8b91669c4d33c63bcdad2448703/packages/flutter_tools/lib/src/build_system/targets/icon_tree_shaker.dart#L29