[llvm] [offload] Extract OMPT out of PluginInterface (PR #221726)

[Jan André Reuter via llvm-commits]

Thyre wrote:

I did some quick tests with this PR, using both `amdgpu` and `x86_64` for testing (i.e. `-fopenmp-targets=x86_64,amdgpu`/`-fopenmp-targets=amdgpu`/`-fopenmp-targets=x86_64`). In all cases I've tested so far, an attached tool seems to still receive all the expected events in the correct order.
In the case of multiple vendors (here `amdgpu` and `x86_64`), the devices also still receive distinct device numbers, allowing a tool to differentiate between all registered devices.

I'll do more thorough testing in the coming days, but wouldn't expect things to significantly break for now.

https://github.com/llvm/llvm-project/pull/221726