Hover events are not receivable in embedded QWindow (macOS)

In our products we reparent a QWindow's underlying native view onto a foreign host window by using QPA's setEmbeddedInForeignView API, which in general works fine.

Since Qt 6.3 however, hover events are not received anymore, as obviously the qnsview is more strictly checked against being a content view, but which is not the case for embedded QWindows (see Details).

The proposed patch reintroduces support for hover events in the embedded use case.

Pick target: 6.3

Details:

• Here (https://code.qt.io/cgit/qt/qtbase.git/tree/src/plugins/platforms/cocoa/qnsview_mouse.mm?h=v6.3.0#n609) the view is checked for being a content view
• If this is not the case, the  {{QCocoaWindow::s_windowUnderMouse }}at https://code.qt.io/cgit/qt/qtbase.git/tree/src/plugins/platforms/cocoa/qnsview_mouse.mm?h=v6.3.0#n616 is not properly setup
•  Which leads to the following check failing, and preventing mouse events to be received: https://code.qt.io/cgit/qt/qtbase.git/tree/src/plugins/platforms/cocoa/qnsview_mouse.mm?h=v6.3.0#n579