Windows: Add ANGLE support.

Windows: Add ANGLE support.

- Add QWindowsEGLContext usable for ANGLE and Windows CE.
- Add QWindowsEGLStaticContext containing the display
  for resource cleanup.
- Add EGLSurface to QWindowsWindow.
- Add a -angle option specifying the path to the external
  ANGLE installation to configure, add libraries to
  the mkspecs.

Initial-patch-by: Jabot Corentin <corentinjabot@gmail.com>
Task-number: QTBUG-24207

Change-Id: I5f80b1efb6996da7c5d70aa3720f7801c9e4c6af
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>
Reviewed-by: Girish Ramakrishnan <girish.1.ramakrishnan@nokia.com>