Implement core wgl functions - wglSwapBuffers - wglCreateContext - wglMakeCurrent These functions are needed by the OpenGL tutorial for Windows desktop Bug: angleproject:3620 Change-Id: I699af63eca4a2c8aaf2c72278a580322410ac499 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1688499 Commit-Queue: Clemen Deng <clemendeng@google.com> Reviewed-by: Geoff Lang <geofflang@chromium.org>