missing coverage for SPIR-V instruction OpImageRead with a non-zero LOD

We are currently missing coverage for the sampler-less image read instruction OpImageRead with an optional LOD image operand, and especially with a non-zero LOD image operand. Since there are no OpenCL C sampler-less read functions that support a non-zero LOD this will likely need dedicated SPIR-V testing.

Testing scenarios:

1. For all implementations supporting SPIR-V, for all supported image types, test OpImageRead with an optional "Level of Detail" equal to zero.
2. For all implementations supporting SPIR-V and cl_khr_mipmap_image, test OpImageQueryLod with a mipmap image, with "Level of Detail" ranging from zero to the number of mipmaps in the image.

* TBD: What is the expected behavior for out-of-range levels of detail?
* TBD: We may also need to specify what the mipmap-related sampler properties should be for OpImageRead, specifically for the mip filter mode, LOD min, and LOD max.

Start by locating the existing SPIR-V image instruction coverage and its test entry points. Add coverage for OpImageRead with optional zero and non-zero LOD values, plus OpImageQueryLod across supported mipmap levels and implementations; clarify the out-of-range and mipmap sampler-property behavior before treating the work as done.

Written by the indexing model from the issue text.