[clang] [Clang][AMDGPU] Add a new builtin type for buffer rsrc (PR #94830)

[Shilei Tian via cfe-commits]

shiltian wrote:

> how does a user initialize/populate this type of objects? by calling a builtin function?

yes. The builtin functions will come next.

https://github.com/llvm/llvm-project/pull/94830