GAPI (fluid): optimization of Separable filter (#13221)
* GAPI (fluid): Separable filter: performance test
* GAPI (fluid): enable all performance tests
* GAPI: separable filters: alternative code for Sobel
* GAPI (fluid): hide unused old code for Sobel filter
* GAPI (fluid): especial code for Sobel if U8 into S16
* GAPI (fluid): back to old code for Sobel
* GAPI (fluid): run_sepfilter3x3_impl() with CPU dispatcher
* GAPI (fluid): run_sepfilter3x3_impl(): fix compiler warnings
* GAPI (fluid): new engine for separable filters (but Sobel)
* GAPI (fluid): new performance engine for Sobel
* GAPI (fluid): Sepfilters performance: fixed compilation error
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