dispatch: attach the appropriate memory qualifiers

We consider all descriptors to be 'restrict'-qualified, because there just plain is no use case we have for aliasing different descriptors. Readonly/writeonly is alreayd handled by the descriptor access mode, so no need to duplicate those memory qualifiers either.

The only ones left are 'coherent', which is required for the peak detection shader's memory barriers to work, and 'volatile', which we don't use. Might have a use for it in the future though, especially for development purposes.

Slight performance gain for compute shaders (especially AV1 grain), but more importantly, fixes a bug.