This reverts commit 50e7d891.

This fixes a problem with the macOS key handling where a flagsChanged event is being sent to a keyDown selector.

Rolls the fuchsia toolchain from
3aa8e071dd1ae7e9fb9e28fa9fcdb9f9fdb7aa06 to 2c0536b76b35fa592ac7b4a0e4bb176eaf55af75

Fix engine in preparation for implementing https://github.com/dart-lang/language/issues/1274 (#23131)

When https://github.com/dart-lang/language/issues/1274 (Infer
non-nullability from local boolean variables) is implemented, flow
analysis will detect that code like this no longer needs to perform a
null check:

    final bool hasIdentityTransform =
        transform == null || isIdentityFloat32ListTransform(transform);
    ...
    if (!hasIdentityTransform) {
      ... transform! ... // Null check unnecessary
    }

To avoid a build failure due to the unnecessary null check, we need to
temporarily write it in a way that we can ignore it.  Once the feature
is complete and rolled into flutter, I'll remove the null check
entirely.

Bug: https://github.com/flutter/flutter/issues/72321Co-authored-by: NJody Sankey <jsankey@google.com>

* Add missing sdk constriants in pubspec.yaml files.

* Update tools/android_lint/pubspec.yaml
Co-authored-by: NZachary Anderson <zanderso@users.noreply.github.com>

Renames from isDown to is_down in accordance with the C++ style guide.