convert-to-sampled-image pass converts images and/or samplers with
given pairs of descriptor set and binding to sampled image.
If a pair of an image and a sampler have the same pair of descriptor
set and binding that is one of the given pairs, they will be
converted to a sampled image. In addition, if only an image has the
descriptor set and binding that is one of the given pairs, it will
be converted to a sampled image as well.
For example, when we have
%a = OpLoad %type_2d_image %texture
%b = OpLoad %type_sampler %sampler
%combined = OpSampledImage %type_sampled_image %a %b
%value = OpImageSampleExplicitLod %v4float %combined ...
1. If %texture and %sampler have the same descriptor set and binding
%combine_texture_and_sampler = OpVaraible %ptr_type_sampled_image_Uniform
...
%combined = OpLoad %type_sampled_image %combine_texture_and_sampler
%value = OpImageSampleExplicitLod %v4float %combined ...
2. If %texture and %sampler have different pairs of descriptor set and binding
%a = OpLoad %type_sampled_image %texture
%extracted_image = OpImage %type_2d_image %a
%b = OpLoad %type_sampler %sampler
%combined = OpSampledImage %type_sampled_image %extracted_image %b
%value = OpImageSampleExplicitLod %v4float %combined ...
