Fixes to make WGL implementation work with OpenGL tutorial
- Give directive parser the correct shader spec when on Desktop GL
- Minor changes to parse Desktop GL shaders
- Moved clientType parameter from Context to Context->mState
- Minor fixes to WGL functions

Bug: angleproject:3666
Change-Id: I01ddb828f6d581ad445f49942589436849eae5d9
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1693244
Commit-Queue: Clemen Deng <clemendeng@google.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>