Win32 GL: Also force not to use depth/stencil/accum bits on legacy contexts (for issue #6401)

Hi,

This attempts to make the updates for #6401 (closed) more complete for legacy contexts (and thus the "base" WGL context used for creating WGL contexts with attributes) that we create more complete by requesting no stencil and accumulation bits, and if possible, depth bits, for our legacy context, that we create via a PIXELFORMATDESCRIPTOR. This also takes into account where some drivers enforce creating contexts with depth bits, so we retry in this case if a pixel format couldn't be acquired with no depth bits.

With blessings, thank you!