[lexical] Bug Fix: Fix selected text not properly deleted after IME input on Safari (macOS)

[sKawashima]

Description

In Safari on macOS, after confirming IME composition (e.g. Japanese input) with a non-backspace key (Enter, Space, etc.), pressing Backspace to delete a text selection (created via Shift+Arrow or Cmd+A) did not work correctly.

Root cause:

Safari fires compositionend before keydown (unlike other browsers).
isSafariEndingComposition is set to true on compositionend to defer composition finalization to the next keydown. However, the flag was only cleared when keydown fired with Backspace — leaving it as stale true when composition was confirmed with any other key.

When the user later pressed Backspace to delete a selection:

1. $handleKeyDown saw isSafariEndingComposition = true and called $onCompositionEndImpl
2. $updateTextNodeFromDOMContent called selection.setTextNodeRange(anchorNode, anchorOffset, anchorNode, focusOffset), forcing anchor and focus onto the same node
3. For multi-node selections (e.g. Cmd+A spanning multiple paragraphs), this corrupted the selection
4. The reconciler updated the DOM selection to match the corrupted Lexical selection
5. The subsequent beforeinput deleteContentBackward operated on the wrong selection, producing incorrect deletion

Fix: When isSafariEndingComposition is true but the key is not Backspace, clear the flag without calling $onCompositionEndImpl. Composition finalization for non-backspace confirmations is already handled by the beforeinput event.

Closes #8153

Test plan

Before

After typing with Japanese IME and confirming with Enter, selecting all text with Cmd+A and pressing Delete does not delete the selected text correctly.

2026-02-19.21.37.49.mov

After

Deletion works correctly after IME composition confirmed with non-backspace
keys.

2026-02-19.22.10.23.mov

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Project	Deployment	Actions	Updated (UTC)
lexical	Ready	Preview, Comment	Feb 19, 2026 1:41pm
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