Improve handling of navigation keys in typing state

[ejbiker93ss]

Refactor typing state management to handle navigation keys correctly.

[indent-staging]

Issues

1 potential issue found:

• Modifier-only keypresses (Shift, Ctrl, Alt, Meta) are not in the navigation key list, so pressing a modifier alone after 800ms idle will trigger the isTyping state and toggle spellcheck, potentially causing the same cursor-reset issue this PR aims to fix. This is a minor edge case since modifier-only keydowns are uncommon in isolation.

Summary

This PR fixes a UX bug where pressing navigation keys (Home, End, arrow keys, PageUp, PageDown) in the composer editor after 800ms of typing inactivity would cause the keypress to be "swallowed." The root cause was that toggling the spellCheck attribute on a contenteditable element causes Chromium to reset the cursor/selection, and navigation keys were incorrectly triggering this toggle.

• Navigation keys are now excluded from triggering the isTyping state transition, preventing unnecessary spellcheck attribute toggling
• Navigation keys no longer reset the 800ms debounce timer (_onDoneTyping), so they don't extend the typing window
• The next() call still executes unconditionally, ensuring Slate's default key handling is always invoked

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Ben Rule

[ejbiker93ss]

Tested and working on my machine 😉

[indent-staging]

Modifier-only keys not excluded: Pressing Shift, Ctrl, Alt, or Meta alone doesn't produce text but will still trigger the isTyping transition and spellcheck toggle. Consider adding 'Shift', 'Control', 'Alt', 'Meta' to this list (and possibly renaming it to isNonTypingKey) to avoid the same cursor-reset issue for these keys. The practical impact is small since standalone modifier presses are uncommon, but it would make the fix more complete.

[bengotow]

This looks great, this was definitely an oversight when we switched to this approach. Thanks!

[ejbiker93ss]

@bengotow , thank you for the quick action here!

[foundry376-bot]

This pull request has been mentioned on Mailspring Community. There might be relevant details there:

https://community.getmailspring.com/t/cant-go-to-start-end-of-the-line-with-home-end-keys/14291/3