This fixes this stupid bug and flicker that we would always select the
first entry when opening context menus for A11y reasons even when A11y
is disabled for the entire window. I call it a bug because it adds
nothing, flickers, and has annoyed me since this was introduced.

Release Notes:

- Fixed an issue where upon opening a context menu, the first entry
would be selected with a delay.
- [GPUI] Added method to query whether A11y support is forcefully
disabled for the current app.