Reland No.2 "Hardware Keyboard: Android"

[dkwingsmt]

Relands #33113, which was reverted due to possible internal breakages.

Changes based on original PR: (See latest commits)

• Fix the algorithm to improvise physical keys and logical keys, and add corresponding tests.

I have tested this PR on g3 (with necessary modifications due to problems of the rolling script.)

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This PR implements the embedder keyboard responder of the Android embedding, the backend of HardwareKeyboard on Android. This is the last platform to support it.

The behaviors are tested on a ChromeOS over ARC++. There are some weird behaviors, mostly for metaState, which are very likely the fault of ARC++ or Android. Therefore the synchronization logic is implemented in a loose way.

There are a few known issues:

• I haven't had chance to test the character combination yet (due to the next item). I just used the same mechanism of the channel embedder.
• [Android] After focusing on a text field, no printable key events can be received ever flutter#104031

This PR assigned a new code plane kLogicalPlane for the physical keys that are improvised from the logical keys.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• 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.
• 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 ///).
• I signed the CLA.
• All existing and new tests are passing.

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[gspencergoog]