[llvm] [OFFLOAD] Add support for indexed per-thread containers (PR #164263)

[Kevin Sala Penades via llvm-commits]

https://github.com/kevinsala approved this pull request.

I'm still not convinced of the `table`/`container` names, and the extra field `NElements`/`size`. But I think it can be fixed in another PR later.

LGTM now.

https://github.com/llvm/llvm-project/pull/164263