Hardware Keyboard: Android

[dkwingsmt]

Description

This PR contains the Android changes for the Hardware Keyboard project.

Related Issues

• Depends on: Hardware Keyboard: Windows #23465
• Umbrella: ☂️ Device-specific keyboard events should happen in the embedder flutter#44918

Tests

I added the following tests:

Replace this with a list of the tests that you added as part of this PR. A
change in behaviour with no test covering it will likely get reverted
accidentally sooner or later. PRs must include tests for all
changed/updated/fixed behaviors. See testing the engine for instructions on
writing and running engine tests.

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]). This will ensure a smooth and quick review process.

• I read the contributor guide and followed the process outlined there for submitting PRs.
• I signed the CLA.
• I read and followed the C++, Objective-C, Java style guides for the engine.
• I read the tree hygiene wiki page, which explains my responsibilities.
• I updated/added relevant documentation.
• All existing and new tests are passing.
• I am willing to follow-up on review comments in a timely manner.

Reviewer Checklist

• I have submitted any presubmit flakes in this PR using the engine presubmit flakes form before re-triggering the failure.

Breaking Change

Did any tests fail when you ran them? Please read handling breaking changes.

• No, no existing tests failed, so this is not a breaking change.
• Yes, this is a breaking change. If not, delete the remainder of this section.
  • I wrote a design doc: https://flutter.dev/go/template Replace this with a link to your design doc's short link
  • I got input from the developer relations team, specifically from: Replace with the names of who gave advice
  • I wrote a migration guide: https://flutter.dev/go/breaking-changes-template Replace this with a link to a pull request that adds the migration guide to https://flutter.dev/docs/release/breaking-changes

[dkwingsmt]

Closing this PR. The keyboard manager has been implemented by #25628 and the embedder handler will be handled some other time.