1. Drop the use of UBOs and SSBOs; since not only are there unaddressed
   packing concerns, but they also don't really provide an advantage.
   Instead, use regular uniform floats (i.e. input variables with
   dim_v), but only do this by default if we have global inputs.

2. Implement the missing case (SH_LITERAL)

3. Improve the signature for the `fill` function.

On my nvidia hardware, both SH_LITERAL and SH_UNIFORM sadly explode for
large inputs - SH_UNIFORM exhausts the UBO size limits when using
vulkan, mainly due to the vec4/float packing inefficiency. SH_LITERAL on
the other hand just makes the nvidia shader compiler explode. Further
investigation is required, but for small LUTs it should work
nonetheless.