video_filter: add egl_surfacetexture filter plugin
On Android, this filter allows to render OpenGL filters to an Android SurfaceTexture.
Contrary to egl_pbuffer, the resulting picture stays on the GPU (it is not downloaded to main memory), providing much better performances.
Was submitted to the ML before the switch to MR: https://mailman.videolan.org/pipermail/vlc-devel/2021-April/143185.html