fix(ios): cross-paragraph keyboard rules

[jahorton]

Fixes #10761.

Turns out my concerns in that issue were well-founded; rules crossing a context-window boundary were not being properly applied. Fortunately, it only takes a couple of small tweaks to fix that... as well as can be done under iOS constraints given 17.0.

Limitations:

• If a surrogate pair exists out-of-context that would be deleted by such a rule, an extra character will be deleted.
• If a combining character exists out-of-context that would be deleted by such a rule, an extra character will be deleted.

To "do better" would require us to track our own version of a context window manually on the iOS side that slides, rather than "jumping" upon a new paragraph start. This is only an idea at this stage, though; it's also certainly too big a project to tackle during the beta cycle.

Given these limitations, I'm not opposed to rejecting this PR at this time due to what is essentially an incomplete solution - those caveats may matter greatly for some scripts and/or languages.

User Testing

TEST_CROSS_PARAGRAPH_RULES: Use the provided specialized test keyboard to verify that the last a-z character is properly rotated by the "rota" key.

Specialized test keyboard: https://jahorton.github.io/last_alphanumeric_rotater.kmp
Source: last_alphanumeric_rotater.zip

• Should this be added to common/test/keyboards? (For desktop use, the 'rota' key is K_BKSLASH.)

1. Install the test keyboard package.
2. With it installed, type 'a', then hit the ENTER key twice.
3. Tap the "rota" key repeatedly. The original a should rotate to b, then c, etc until reaching z. After z, it will return to a.
4. If any other effects occur, FAIL this test.

[keymanapp-test-bot]

User Test Results

Test specification and instructions

• ✅ TEST_CROSS_PARAGRAPH_RULES (PASSED): Tested with the attached PR build 17.0.280-beta-test-10905 on an iPhone 13 Mobile device and here is my observation: 1. Installed last_alpharnumeric_rotater keyboard. 2. Typed 'a', then hit the ENTER key twice. 3. Clicked the "rota" key repeatedly and verified that it reached the z key then returned to show a key. Seems to be working as expected.

Test Artifacts

• iOS
  • Keyman for iOS (simulator image)
  • FirstVoices Keyboards for iOS (simulator image)
  • TestFlight internal PR build version - 17.0.280 (0.10905.10479)

[mcdurdin]

I think this change makes sense for robustness, even if we want to go further in the future.

LGTM

[bharanidharanj]

Test Results

• TEST_CROSS_PARAGRAPH_RULES (PASSED): Tested with the attached PR build 17.0.280-beta-test-10905 on an iPhone 13 Mobile device and here is my observation: 1. Installed last_alpharnumeric_rotater keyboard. 2. Typed 'a', then hit the ENTER key twice. 3. Clicked the "rota" key repeatedly and verified that it reached the z key then returned to show a key. Seems to be working as expected.

[keyman-server]

Changes in this pull request will be available for download in Keyman version 17.0.281-beta