[HLSL] Allow __builtin_hlsl_resource_getpointer to take no indices (#195151)

In preperation for adding ConstnatBuffer<T>, we will need to be able to
access the base pointer for the data constat buffer resource handle is
pointingto
to. This is done by:

1. Making the index operand in __builtin_hlsl_resource_getpointer
   optional.
2. Modifing the codegen for __builtin_hlsl_resource_getpointer to emit a
   call to resource.getbasepointer when no index is provided.
3. Add the resource.getbasepointer for the dx and spv targets.

Another issue is that the address space for the pointer returned by
__builtin_hlsl_resource_getpointer is not always hlsl_device any more.
Changes are made to get the correct address space based on the resource
class of the handle.

Note that we cannot implement codegen for
__builtin_hlsl_resource_getpointer directly. The tests for the codegen
changes will be in a follow up PR that add ConstnatBuffer<T>.

Assisted-by: Gemini

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- main
  - https://github.com/llvm/llvm-project/pull/195151 :point_left:
    - https://github.com/llvm/llvm-project/pull/195152
      - https://github.com/llvm/llvm-project/pull/195153
        - https://github.com/llvm/llvm-project/pull/195154

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