Made fire_mouse_event take an enum for event_name
Added an enum with the mouse event options for `fire_mouse_event` and refactored the `event_name` parameter to take the enum as argument.
I also added two options (Leave and Enter) which are noted as todo in the comments.
- [x] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These Changes fix#18943.
- [X] These changes do not require tests because the issue said a clean build suffices.
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