fix(android): handle surrogate pairs in selection range indexing

[jahorton]

Fixes an issue noted while validating #10873.

This change prevents backspaces and context-deletions from keyboard rules from mishandling the context after moving the text insertion point and/or selecting text.

Recent changes to the codebase have resulted in a need to consistently specify selection ranges with non-BMP indexing. #10662 recognized the need to keep non-BMP processing enabled as part of a different Android bug fix, and #10728 took things a bit further (for iOS) while further validating this position. Until now... we missed that Android was actually specifying the selection range with code unit (BMP) indexing, which does not account for surrogate pairs.

User Testing

TEST_POST_EMOJI_ROTATION:

1. Go to https://jahorton.github.io/ and download the test_robust_deletions.kmp package.
   Alternatively, scan this QR code for the package:

   

2. Enable Keyman as system keyboard.

3. Open the device's primary mail app (gmail). If prompted, attempt to sign in with a Gmail account.

   • Note: you don't need to actually sign in, though. The "Sign in" prompt itself is a perfect test target!

4. Type just one of the emoji keys 4 times. (Do not exceed 7.)

5. Type ggg.

6. Select ggg and hit backspace to delete it.

7. Type p once, then continue typing it to verify that 'p' correctly rotates as follows, without affecting any other pre-existing text:
   - 'p' will rotate through: p, ṗ, p̂, p̂p̂, p, ...
   - The number of code points are: 1, 2, 2, 4, 1, ...
   - One backspace should delete one codepoint; therefore, to delete p̂p̂ completely should take 4 backspaces.

[keymanapp-test-bot]

User Test Results

Test specification and instructions

• ✅ TEST_POST_EMOJI_ROTATION (PASSED): Tested with the attached PR build (Keyman 17.0.279-beta-test-10885) on an Android 13 Mobile device and here is my observation: 1. Installed test_robust_deletions.kmp package. 2. Enabled Keyman as the system-wide keyboard. 3. Opened an Gmail account. 4. Typed an emoji keys 4 times. 5. Typed ggg. 6. Selected ggg then hit the backspace key to delete it. Deleted. 7. Typed the 'p' key and entered the letter p on the text field. 8. Verified that the 'p' letter changes with each press of the 'p' key. ie., ṗ, p̂, p̂p̂ 9. On the fourth press of the 'p' key, it deleted the p̂p̂ character and displayed the standard 'p' key. Seems to be working as expected. (notes)

Test Artifacts

• Android
  • Keyman for Android apk
  • FirstVoices for Android 16.0 apk
  • FirstVoices Keyboards for Android apk
  • KeyboardHarness apk
  • Keyman for Android 16.0 apk
  • KMSample1 apk
  • KMSample2 apk

[mcdurdin]

Fixes an issue noted while validating #10873.

Just a process thing, it's better to split that out into a separate issue for tracking in the future.

[mcdurdin]

Changes LGTM

[darcywong00]

Should check icText != null before getting the text.

[darcywong00]

lgtm

[bharanidharanj]

Test Results

• TEST_POST_EMOJI_ROTATION (PASSED): Tested with the attached PR build (Keyman 17.0.279-beta-test-10885) on an Android 13 Mobile device and here is my observation: 1. Installed test_robust_deletions.kmp package. 2. Enabled Keyman as the system-wide keyboard. 3. Opened an Gmail account. 4. Typed an emoji keys 4 times. 5. Typed ggg. 6. Selected ggg then hit the backspace key to delete it. Deleted. 7. Typed the 'p' key and entered the letter p on the text field. 8. Verified that the 'p' letter changes with each press of the 'p' key. ie., ṗ, p̂, p̂p̂ 9. On the fourth press of the 'p' key, it deleted the p̂p̂ character and displayed the standard 'p' key. Seems to be working as expected.

  

[keyman-server]

Changes in this pull request will be available for download in Keyman version 17.0.280-beta