Backported from @haasn's change to libplacebo, except in the current RA,
there's nothing to indicate an ra_format can be bound as a storage
image, so there's no way to force all of these formats to have a
glsl_format. Instead, the layout qualifier will be removed if
glsl_format is NULL.
This is needed for the upcoming ra_d3d11 backend. In Direct3D 11, while
loading float values from unorm images often works as expected, it's
technically undefined behaviour, and in Windows 10, it will cause the
debug layer to spam the log with error messages. Also, apparently in
GLSL, the format name must match the image's format exactly (but in
Direct3D, it just has to have the same component type.)
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