[llvm] [Offload] Introduce offload-tblgen and initial new API implementation (PR #108413)

[Shilei Tian via llvm-commits]

shiltian wrote:

I'm afraid the code style of this entire stuff will be out of control. Looking at the code, there are at least three different code styles. I don't think it's a good idea to keep as it is.

https://github.com/llvm/llvm-project/pull/108413