d3d11: Various code cleanup
d3d11: Privatize d3d11memory implementation
Hide most of symbols of GstD3D11Memory object.
GstD3D11Memory is one of primary resource for imcoming d3d11 library
and it's expected to be a extensible feature.
Hiding implementation detail would be helpful for later use case.
Summary of this commit:
* Now all native Direct3D11 resources are private of GstD3D11Memory.
To access native resources, getter methods need to be used
or generic map (e.g., gst_memory_map) API should be called
apart from some exceptional case such as d3d11decoder case.
* Various helper methods are added for GstBuffer related operations
and in order to remove duplicated code.
d3d11: Add a helper method for d3d11buffferpool setup
Remove duplicated code for d3d11buffferpool setup.
d3d11device: Remove optional helper methods
Most of Direct3D11 APIs can be called without GstD3D11Device
abstraction. This is a part of prework for public GstD3D11 library
to introduce minimal APIs