[Development] Change ANGLE 3rd party source from Google to Microsoft

[Oliver Wolff]

Hi,

I would like to propose a change of where we get the ANGLE sources we 
use in qtbase. At the moment we use Google's ANGLE 
(https://github.com/google/angle). Unfortunately they stopped supporting 
MSVC 2015 last year and their UWP code path does not build out of the 
box. Microsoft (https://github.com/Microsoft/angle) still actively 
maintains MSVC 2015 and also has a focus on UWP within their port. As 
far as I can tell there is no difference in the license used, so we 
should be fine from that point of view.

Background info: ANGLE is used to translate OpenGL calls to Direct 3D. 
This is done for desktop Windows
     - by default (when no "-opengl ..." is given (which arguably should 
be changed to dynamic))
     - if native OpenGL fails (when configured with -opengl dynamic)  
due to crappy opengl drivers or blacklisted GPU for example

Is everyone ok with this change? The ANGLE update from Google (which 
uses a revision that still supports MSVC 2015) would be ready 
(https://codereview.qt-project.org/#/c/233385/), but we would like to 
use a newer version from Microsoft for 5.12 if we can agree on this change.

Best regards,
Olli