[llvm] [DirectX] introducing lowering for `bufferUpdateCounter` (PR #115041)

[Helena Kotas via llvm-commits]

hekota wrote:

@joaosaffran - `updateBufferCounter` needs to return `uint` with the pre-incremented or pre-decremented counter value: 

See https://godbolt.org/z/rGhWbcrY5
https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/sm5-object-rwstructuredbuffer-incrementcounter



https://github.com/llvm/llvm-project/pull/115041