Added some more missing spaces after conditional statements.  Also
made unsupported MSAA_4X an assert instead of an abort and also
removed dpi-aware cases for older OS's.  More changes would be needed
to support those OS versions, namely, removing the dependency
on shcore.

Instead of calling BeginPaint/EndPaint in WM_PAINT which signals to the
OS that our window content is updated, now when we encounter the WM_PAINT
message instead we return back to the raylib application which will
trigger it to render a new frame. We've replaced the call to BeginPaint
and EndPaint with a call to ValidateRect in SwapBuffers, which, means
we're now correctly telling the OS when our window content is actually
up-to-date.

Note that this doesn't fix the window content not being updated during
a window resize/move beacuse thos have their own message loop which
doesn't return early when it's time to paint.

I don't understand OpenGL well enough to know the difference between
SwapBuffers and wglSwapLayerBuffers but the former seems to double
my FPS (from 2000 to about 4000 in core_vr_simulator).