Translate array-of-arrays of resources to Vulkan single-level arrays

Khronos decided that anything in Vulkan that requires a binding should only be a single-dimensional array in SPIR-V.

Glslang could have new functionality to lower arrays-of-arrays by doing flattening arithmetic. However, this functionality is currently missing.

(In the meantime, I will add a warning about the situation.)

The issue names no files, tests, or entry points. Start by locating the compiler path that translates resource arrays to SPIR-V and review existing Vulkan resource-binding tests; done means arrays-of-arrays are lowered to single-level arrays with correct flattening arithmetic.

Written by the indexing model from the issue text.