gl: fix incorrect plugin dependencies

The GL/GLES2 plugins doesn't depends anymore on X11, WAYLAND, VAAPI or other
hardware libs.

Move all converters (that were built in GL plugins) in separate plugins, with a
"glconv" plugin capability. This new type of module will be loaded by GL
plugins when a video format is opaque. Otherwise, the built-in software
converter (that handle RGB,YUV,YXZ12) will be used.

Each new converters plugins depends only on hardware libs like VAAPI-X11,
VAAPI-WL. These news plugins don't depend on Open GL / GLES2. Therefore, one
glconv plugin can be used by a GL and a GLES2 plugin.

Fixes #18575