The `buttons` property on mouse events dispatched by WebAutomationSession is always zero, and does not correctly reflect what mouse button is pressed. I suspect the fix involves swizzling the `+[NSEvent pressedMouseButtons]` like in WKTR/DRT. This will get us to fully pass the pointerevents/pointerevent_attributes_hoverable_pointers.html?mouse WPT.
<rdar://problem/116049187>
Pull request: https://github.com/WebKit/WebKit/pull/18265
Committed 268529@main (e120ba1e5646): <https://commits.webkit.org/268529@main> Reviewed commits have been landed. Closing PR #18265 and removing active labels.