Auto merge of #115753 - tgross35:threadinfo-refactor, r=thomcc

Refactor `thread_info` to remove the `RefCell`

`thread_info` currently uses `RefCell`-based initialization. Refactor this to use `OnceCell` instead which is more performant and better suits the needs of one-time initialization.

This is nobody's bottleneck but OnceCell checks are a single `cmp` vs. `RefCell<Option>` needing runtime logic

Author: bors