Rename SharedKeyboardAndMouseEventInit to EventModifierInit
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- [X] renamed file SharedMouseAndKeyboardEventInit,
- [X] changed SharedKeyboardAndMouseEventInit to EventModifierInit.
- [X] Rebased mozilla/master into it.
- [x] Ran build and tidy test without errors
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix#11611 (github issue number if applicable).
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