opengl: abstract picture storage from renderer (part 1)

MR for CI

Discussion:

• https://mailman.videolan.org/pipermail/vlc-devel/2020-March/thread.html#132236
• https://mailman.videolan.org/pipermail/vlc-devel/2020-March/132236.html

added 14 commits

• b5ea6d79 - opengl: factorize program creation
• 1cd6f799 - opengl: fix unused variable
• 3f878f7d - opengl: move vtable to vlc_gl_api
• 91f7921f - opengl: pass vlc_gl_api instead of virtual table
• 57028c32 - opengl: move fields from interop to gl_api
• c360a6b2 - opengl: expose npot support in gl_api
• b8f0df01 - opengl: convert texture coords in fragment shader
• 57860d39 - opengl: setup coords once for all
• e153e47a - opengl: apply orientation in fragment shader
• 1dfec9e0 - opengl: apply stereo transform using a matrix
• b3087f77 - opengl: merge successive loops
• 294b0288 - opengl: move down vlc_gl_renderer_Prepare()
• de5f46be - opengl: move paddings computation to _Prepare()
• fa08a88e - opengl: remove unused source format parameter

Compare with previous version

changed the description

Merged :)

closed