Retrieve the depth for each component and internal texture format
separately. Only for 8 bit per component textures we assume that all
bits are used (or else we would in my opinion create too many probe
textures).
Assuming 8 bit components are always correct also fixes operation in
GLES3, where we assumed that each component had -1 bits depth, and this
all UNORM formats were considered unusable. On GLES, the function to
check the real bit depth is not available. Since GLES has no 16 bit
UNORM textures at all, except with the MPGL_CAP_EXT16 extension, just
drop the special condition for it. (Of course GLES still manages to
introduce a funny special case by allowing GL_LUMINANCE , but not
defining GL_TEXTURE_LUMINANCE_SIZE.)
Should fix#4749.
Since the GL *gl is no longer needed for the timers, we can get rid of
the sc->gl dependency. This requires moving a utility function (which is
not GL-specific anyway) out of gl_utils.h and into utils.h
In order to prevent code duplication and keep the ra abstraction as
small as possible, `ra` only implements the actual timer queries,
it does not do pooling/averaging of the results. This is instead moved
to a ra-neutral struct timer_pool in utils.c.
Now all GL-specifics of shader compilation are abstracted through ra.
Of course we still have everything hardcoded to GLSL - that isn't going
to change.
Some things will probably change later - in particular, the way we pass
uniforms and textures to the shader. Currently, there is a confusing
mismatch between "primitive" uniforms like floats, and others like
textures.
Also, SSBOs are not abstracted yet.
Actually GL-specific parts go into gl_utils.c/h, the shader cache
(gl_sc*) into shader_cache.c/h.
No semantic changes of any kind, except that the VAO helper is made
public again as part of gl_utils.c (all while the goal for gl_utils.c
itself is to be included by GL-specific code).
