cv::UMat output/input in VideoCapture/VideoWriter (data stays in GPU memory)

* FFMPEG with UMat input/output

* OpenCL_D3D* context

* fix Linux build

* cosmetic changes

* fix build if USE_AV_HW_CODECS=0

* simplify how child context pointer stored in parent context

* QSV interop with OpenCL on Windows

* detect_msdk.cmake via pkg-config

* fix av_buffer_ref() usage

* revert windows-decode-mfx whitelisting; remove debug msg

* address review comments

* rename property to HW_ACCELERATION_USE_OPENCL

* fix issue with "cl_khr_d3d11_sharing" extension not reported by OpenCL GPU+CPU platform

* core(ocl): add OpenCL stubs for configurations without OpenCL

* videoio(ffmpeg): update #if guards

* Put OpenCL related code under HAVE_OPENCL; simplify reuse of media context from OpenCL context

* videoio(test): skip unsupported tests

- plugins don't support OpenCL/UMat yet
- change handling of *_USE_OPENCL flag

* videoio(ffmpeg): OpenCL dependency

* videoio(ffmpeg): MediaSDK/oneVPL dependency

* cleanup, logging

* cmake: fix handling of 3rdparty interface targets
Co-authored-by: NAlexander Alekhin <alexander.a.alekhin@gmail.com>