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

[Thorsten Schütt via llvm-commits]

tschuett wrote:

* On your machine is probably a file called arm_sve.h. Surprise it is tablgened, but easy to read.
* If you are eager to checkin auto-generated files, then maybe tblgen is not the right tool for you.
* Maybe you have to improve your tblgen tool, to make the output look nicer.

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