WinRT: made OpenGL window-init work with latest round of ANGLE/WinRT updates Various constants in ANGLE/WinRT, both in MSOpenTech's ms-master branch, and in Google's branch, were changed again. This change makes SDL/WinRT work with them. To note, the ms-master branch (of ANGLE) was updated via this merge: https://github.com/MSOpenTech/angle/commit/bbd2eb0a9c453a941f2c7abacf616d5a66b6be92#diff-d1377fbe747de154e1bfcf7221d3de67

WinRT: another ANGLE/OpenGL-initialization, error messaging tweak

WinRT: ANGLE/OpenGLES-initialization, error message improvements

Updated name of assert type in test program.

Cleaning out a silly coding style I used to use. Changed all the "return (x);" lines to "return x;"

Removed an unnecessary #ifdef.

Updated internal documentation comments.

Windows: Fixed ignoring return value of internal function. If the function WIN_ConvertUTF32toUTF8() failed (should currently not be possible) a not terminated string would have been sent as text input event. This also fixed converting characters more often than needed on key repetition.

Emscripten: Fixed ignoring return value of internal function. If the function Emscripten_ConvertUTF32toUTF8() failed (should currently not be possible) a not terminated string would have been sent as text input event.

Emscripten: Partially fixed not removing key event callbacks if hint was used. The key event callbacks were always removed from the same target although it is possible to set them to different targets using the hint. This is only a partial fix because it assumes that the hint is not changed to a different value later.