Track whether a keydown should perform text insertion separately from
the delivered code point. Native frontends and text-oriented test paths
can now mark events that came from text input, while shortcut-style key
events keep Alt-modified default insertion suppressed.
This lets macOS Option-generated text such as Option+A and Option+Space
insert into editable controls without making plain Alt shortcuts insert
their base character. Add coverage for Alt text, Ctrl+Alt text,
separator text, Ctrl-only shortcuts, and Alt shortcuts.
Trackpad pinches applied directly as visual viewport zoom, so pages
could not observe the gesture or cancel the browser default. Canvas
apps such as maps expect the ctrl-wheel path instead.
