Add conversion functions from native modifier types to OptionSet<WebKit::WebEventModifier>. On macOS this is NSEventModifierFlags, and on iOS this is UIKeyModifierFlags.
<rdar://problem/102571520>
Pull request: https://github.com/WebKit/WebKit/pull/6701
Committed 256942@main (8996a7f84e0f): <https://commits.webkit.org/256942@main> Reviewed commits have been landed. Closing PR #6701 and removing active labels.