[SPIR-V] Fix bug using `Texture2D` with alias template for `SpirvType`

Description
For the (currently unmerged) SpirvType PR, Texture2D (and presumably other built-in types) cannot be used as an argument to an alias template for SpirvType

Steps to Reproduce

Compile

template<typename SomeType, uint Length>
using Array = vk::SpirvOpaqueType</* OpTypeArray */ 28, SomeType, vk::integral_constant<uint, Length> >;

void main() {
  Array<Texture2D, 4> image;
}

With the command

dxc -T ps_6_0 -E main -spirv

Actual Behavior
Error:

foo.hlsl:2:1: error: 'Texture2D<vector<float, 4> >' is an object and cannot be used as a type parameter
using Array = vk::SpirvOpaqueType</* OpTypeArray */ 28, SomeType, vk::integral_constant<uint, Length> >;
^
foo.hlsl:5:3: note: in instantiation of template type alias 'Array' requested here
  Array<Texture2D, 4> image;
  ^

Environment

• DXC version libdxcompiler.so: 1.8(dev;4545-a97b48a5) (development version of #6156)
• Host Operating System Linux