HLSL: unwanted implicit conversion from Texture2DArray to Texture2D

Hi,

The following code is rejected by fxc and dxc.
However, it is accepted by glslang - which will produce invalid SPIR-V code, if one tries to access `texture` in `f`.

```
void f(Texture2D texture) {}
void g(Texture2DArray array) { f(array); }
```

https://shader-playground.timjones.io/85b34b00156e57adb4bd6c401925fb7c

Start by reproducing the reported Texture2DArray-to-Texture2D conversion with glslang and compare its behavior with fxc and dxc. Trace the HLSL type-checking and conversion handling, then add coverage for the snippet; done means the invalid implicit conversion is rejected and cannot produce invalid SPIR-V.

Written by the indexing model from the issue text.