[PATCH 0/6] MR846: uiautomationcore: Implement basic HWND based HUIANODE behavior. (v2)

[Connor McAdams (＠cmcadams)]

Changes since prior MR:
- Check if HWND is valid after sending `WM_GETOBJECT` and getting a 0 return value.
- Block on thread calling `UiaNodeFromHandle()` rather than the marshaling thread.
- Squash `IWineUiaNode::get_prop_val` commit into commit where it is actually used.