video_filter: opengl/egl_pbuffer: bring support for GLES2 on Linux

Use the correct OpenGL flavour (GLES or OpenGL) at runtime by providing both capabilities, fixing the usage of OpenGL filters through GLES2 on Linux where both are supported.

The OpenGL ES2 filter has the same shortcut name as the OpenGL filter, which I'm still a bit unsure about since it creates fallback on OpenGL filter failure, but there are guenuine reasons why it could fail on OpenGL but not on OpenGL ES, like the presence of an extension like the support for GL_OES_EGL_image_external or the non-support of anything else but OpenGL ES with a given version.