[HLSL] Should `__decltype` drop address space qualifiers from an array prvalue?

Discovered in #198698. Related to [CWG1261](https://cplusplus.github.io/CWG/issues/1261.html).

A naive fix of #198580 that more consistently applies the resolution of [CWG1261](https://cplusplus.github.io/CWG/issues/1261.html) makes `__decltype` keep the address space qualifier for an array prvalue in HLSL. However, the test added in #133508 relied on that `__decltype` drops qualifiers from an array prvalue.

I don't know whether it's better or worse to generalize the resolution of [CWG1261](https://cplusplus.github.io/CWG/issues/1261.html) to address space qualifiers.

Start by reading the linked discussions for #198698, #198580, and #133508, then review the CWG1261 resolution. Determine whether HLSL __decltype should retain address-space qualifiers on array prvalues; done requires an agreed semantic direction and corresponding implementation and test changes, but no relevant files or test paths are named here.

Written by the indexing model from the issue text.