As described in https://github.com/flutter/flutter/issues/121684, we currently have inconsistencies between Flutter SDK constraints and Dart SDK constraints; we have often updated only the former. This PR:
1. Adds CI enforcement via the repo tooling that the minimum versions are consistent.
2. Adds a new repo tooling command to update SDK constraints, to help mass-fix all the violations of the new enforcement in step 1 (and for future mass changes, such as when we update our test matrix and mass-drop support for versions that are no longe tested).
- In all cases, the looser constraint was updated to match the more restrictive constraint, such that there's no actual change in what Flutter version any package actually supports.
3. Runs `dart fix --apply` over all changed packages to automatically fix all of the analysis failures caused by step 2 suddenly making all of our packages able to use `super` parameters.
Fixes https://github.com/flutter/flutter/issues/121684
Fixes https://github.com/flutter/flutter/issues/121685
