Fixes#18808
Previously, the triggeredByAccelerator flag would be entirely coupled with whether or not the modifier keys were being used or not.
This PR swaps out the ui::EventFlagsFromModifiers([event modifierFlags])) call in the macOS code to ui::EventFlagsFromNSEventWithModifiers(event, [event modifierFlags])). The latter outputs flags that take into account mouse click events on top of modifier flags (see Chromium documentation).
The business logic to detect triggeredByAccelerator is then changed to exclude any mouse click flags.
* chore: use ScopedPumpMessagesInPrivateModes in tray
* revert refcounting of AtomMenuModel
* Prefer WeakPtr for posting tasks to handle unexpected destruction
