fix: non-client mouse events on WCO-enabled windows

[clavin]

Description of Change

My change in #32672 caused a regression where WCO-enabled windows (on Windows) could no longer be dragged. This is because in HWNDMessageHandler::HandleMouseEventInternal, HandleMouseEvent (which is what I patched in the previous PR) is called before HandleMouseInputForCaption (which is where the dragging happens I think, from testing). Instead of trying to patch in something to move the marking of the event as handled further down, I opted instead to try and fix the issue with LegacyRenderWidgetHostHWND.

This PR introduces a patch that does two things, particularly only for WCO-enabled windows right now:

1. Correctly track non-client mouse events, not just regular mouse events. This is mostly just some boilerplate to include those messages.
2. Instead of falling through to DefWindowProc using the parent window handle (GetParent()), it is instead called on its own window handle. This seems to avoid the issue with a mysterious WM_NCMOUSELEAVE message being generated by the DefWindowProc.
3. (It also reverts my changes in the previous PR.)

This should be safe to do since the LegacyRenderWidgetHostHWND doesn't normally cover the non-client area in windows without hidden title bars (thus never reaching this code) and for frameless windows this is the same code path. Thus the change should only apply to WCO-enabled windows. I also think the code is still correct since it is the job of LegacyRenderWidgetHostHWND to forward messages to its parent window anyways.

I know this is a patch which we usually try to avoid those, however I don't really see an alternative for either possible solution without making a patch. I'll try to upstream this, but if that fails the only other way to remove this patch would be when LegacyRenderWidgetHostHWND is finally removed (see its header comments for more info on that; doesn't look very defined though).

Checklist

• PR description included and stakeholders cc'd
• npm test passes (letting CI check)
• tests are changed or added
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Fixed drag regions on WCO windows on Windows

[release-clerk]

Release Notes Persisted

Fixed drag regions on WCO windows on Windows

[trop]

I have automatically backported this PR to "15-x-y", please check out #33199

[trop]

I have automatically backported this PR to "16-x-y", please check out #33200

[trop]

I have automatically backported this PR to "17-x-y", please check out #33201

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I have automatically backported this PR to "18-x-y", please check out #33202