This adds a LICENSE file to the packages/flutter directory so that it can be found when building, and a test to make sure it exists in produced binaries.

Makes the following changes to the behavior of precache:
- The --all-platforms flags now fetches all artifacts, rather than just
  turning off platform filtering of selected artifacts.
- Explicitly requested artifacts are no longer subject to platform
  filtering. E.g., 'precache --ios' will download iOS artifacts on
  Windows and Linux (but 'precache' without an 'ios' flag will still
  only download iOS artifacts on macOS).
- Desktop platform artifacts now respect the bypassing of platform
  filtering.

Fixes #53272

2b37d1d46 Roll src/third_party/skia 7a3358c80b6e..0f5e7581a004 (1 commits) (flutter/engine#17444) (#53757)

This reverts commit aee9e94c.

767b48abc Roll src/third_party/dart 0f89df0c00e7..eea97179386a (3 commits) (flutter/engine#17443) (#53744)

* Date Picker should honor DialogTheme shape, and elevation.

Adds a VisualDensity.adaptivePlatformDensity static function that returns different values for visual density based on the defaultTargetPlatform. Returns compact for desktop platforms, and a default visual density for other platforms.

This reverts commit e71cf1cd.

* Update stack trace test expectations to adjust for a fix landed in dart sdk

* Include engine roll to 10887c2abe7b7fe5866e84d6b63dd546f02fc963

* Update column for the exception expectation