Fix iOS TextField cursor placement on CJK punctuation

[Kyle (Kyle-Ye)]

Tapping CJK punctuation in an iOS TextField can move the caret to a later
whitespace instead of keeping it near the tapped character.

For example, tapping 、 at offset 6 in the reproduction attached to
CMP-10699 moves the selection to offset 130.

determineCursorDesiredOffset treats punctuation as part of Cupertino's
Latin word-snapping behavior. CJK punctuation therefore enters
findNextNonWhitespaceSymbolsSubsequenceStartOffset and may scan across
the following CJK text until it reaches the next whitespace.

Keep character-level cursor placement for CJK scripts and full-width forms
before applying the existing Latin word adjustment. Both
BasicTextField(TextFieldValue) and BasicTextField(TextFieldState) use
this shared iOS path. Android behavior is unchanged.

Fixes https://youtrack.jetbrains.com/issue/CMP-10699

Testing

• Added a regression test for tapping U+3001 IDEOGRAPHIC COMMA.
• Added tests covering CJK scripts, full-width forms, Latin punctuation,
  emoji, supplementary CJK characters, and invalid offsets.
• Ran:
  ./gradlew :compose:foundation:foundation:iosSimulatorArm64Test
• Verified with the reproducer on iPhone 14 / iOS 26.0:
  the selection remains at offset 6 instead of jumping to 130.

Release Notes

Fixes - iOS

• Fixed the TextField caret jumping to a later whitespace when tapping
  CJK punctuation.

Google CLA

Signed the Google Contributor License Agreement.

[Andrei Salavei (ASalavei)]

Comment says about iOS only. Is it applicable for Desktop and Web as well?

cc Alexander Maryanovsky (@m-sasha) , Oleksandr Karpovich (@eymar)

[Kyle (Kyle-Ye)]

No, the behavior change is iOS-specific IMO.

requiresCharacterLevelCursorPlacement is defined in skikoMain because
the existing Cupertino cursor adjustment and its tests live there, but
determineCursorDesiredOffset only has iOS production call sites:

• the legacy TextField path through TextFieldPointerModifier.ios.kt
• the state-based TextField path through TextFieldSelectionState.ios.kt

Desktop, Web, and macOS use defaultTextFieldPointer and do not invoke this
logic, so their cursor behavior is unchanged.

[Oleksandr Karpovich (eymar)]

It's also used in internal fun TextFieldDelegate.Companion.cupertinoSetCursorOffsetFocused which is in skikoMain.

But in the end it's iosMain only.

LGTM from web perspective (not affecting web).

[Kyle (Kyle-Ye)]

Could you please trigger the CI workflows for this PR? Andrei Salavei (@ASalavei)

And is there a process for regular external contributors (I’ve previously had #3183 and #3203 merged) to become trusted for CI purposes so that future fork PR workflows no longer require manual approval?

[Andrei Salavei (ASalavei)]

The range inside the requiresCharacterLevelCursorPlacement includes U+3000 IDEOGRAPHIC SPACE (Unicode Zs). The new branch runs before isWhitespaceOrPunctuation, so tapping a fullwidth space now leaves the caret on the space instead of moving to the next word.

I would consider moving this check after the currentText.isWhitespaceOrPunctuation(offset)