st/wgl: Don't rely on GDI to bookkeep pixelformat for us.

This allows to use apitrace's retracediff script on Windows to retrace and
compare two builds of a Mesa based opengl32.dll/ICD side-by-side.

See also https://github.com/apitrace/apitrace/commit/e4a4f15f5b92e0abbd24d7d053da25f8278c9f64
2 files changed