Address access sanitation

[kvark]

We need a way of modifying the SPIR-V so that no resource access goes beyond the bounds, for the sake of GPUWeb security. Some of the checks could be omitted by doing a static analysis, but a general approach could be injecting the code that queries buffers/images dimensions and reset the address offset to 0 using a dynamic check for that address to be in the bounds.

[kvark]

@dneto0's experimental code in SPIRV-Tools: https://github.com/dneto0/SPIRV-Tools/tree/robust-access

[antiagainst]

Cool! I'll take a look and find some time to working on rspirv.

Been quite absorbed by SPIR-V CodeGen in DirectXShaderCompiler recently. :)