Add support for debug markers via D3DPERF API and KHR_debug. This makes
it easier to understand RenderDoc captures.
D3DPERF is preferred to ID3DUserDefinedAnnotation because it supports
colors. d3d9.lib is now linked in to support this.
This feature is disabled by default, and is controlled by
GS_USE_DEBUG_MARKERS.
From: obsproject/obs-studio#1799