d3d11compositor: Performance optimization

d3d11compositor: Performance optimization

Removing glvideomixer-like nuance (it was initially referenced)
and rewriting element since it's not an optimal design at all
from performance point of view.

* Remove wrapper bin (and internal conversion/upload/download elements)
  which will waste CPU/GPU resources. Conversion/blending can be done by the
  d3d11compositor element at once.
* Add support YUV blending without RGB conversion.
  The RGB <-> YUV conversion is completely unnecessary since YUV textures
  support blending as well.
* Remove complicated blending operation properties since it's hard
  to use from application point of view. Instead, adding "operator" property
  like what compositor element does.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2631>