spirv-val "Assertion failed" when an AccelerationStructure handle is put inside a uniform buffer

I've been working on adding support for ray tracing to [my shader EDSL](https://gitlab.com/sheaf/fir) which compiles directly to `SPIR-V`.

I assumed that one was allowed to store an `AccelerationStructure` handle in structures, and that it would behave like a 64-bit unsigned integer. I presume that's actually not permitted (could someone point to the relevant part of the `SPIR-V` specification? I must have missed it). At any rate, it triggers the following assertion failure:

> Assertion failed: 0, file ..\source\val\validate_decorations.cpp, line 225

I believe `spirv-val` should throw an error in this case rather than an assertion failed.

Start in source/val/validate_decorations.cpp at line 225 and inspect the validation path reached when an AccelerationStructure handle is placed in a uniform-buffer structure. Reproduce the reported spirv-val failure using the SPIR-V generated by the linked shader EDSL, then verify that invalid input produces a validation diagnostic instead of an assertion failure.

Written by the indexing model from the issue text.