https://skia-review.git.corp.google.com/c/skia/+/656237 changed how some GPU files are #included Skia-side, which revealed some missing forward declares and #includes in Flutter.

These are not the minimal set of changes needed to fix the current issue; some of them were found via git grep and are trying to proactively address issues that will arise as Skia continues to re-organize its codebase.

Pre-launch Checklist

• [ x ] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [ x ] I read the Tree Hygiene wiki page, which explains my responsibilities.
• [ x ] I read and followed the Flutter Style Guide and the C++, Objective-C, Java style guides.
• I listed at least one issue that this PR fixes in the description above.
• [ x ] I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test-exempt. See testing the engine for instructions on writing and running engine tests.
• I updated/added relevant documentation (doc comments with ///).
• [ x ] I signed the CLA.
• All existing and new tests are passing.

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