Rollup merge of #143051 - Stypox:tracing-validity, r=RalfJung

Add tracing to `validate_operand`

This PR adds a tracing call to keep track of how much time is spent in `validate_operand` and `const_validate_operand`. Let me know if more fine-grained tracing is needed (e.g. adding tracing to `validate_operand_internal` too, which is just called from those two functions).

I also fixed the rustdoc of `validate_operand` and `const_validate_operand` since it was referencing an older name for the `val` parameter which was renamed in cbdcbf0d6a586792c5e0a0b8965a3179bac56120.

Here is some tracing output when Miri is run on `src/tools/miri/tests/pass/hello.rs`, visualizable in [ui.perfetto.dev](https://ui.perfetto.dev/): [trace-1750932222218210.json](https://github.com/user-attachments/files/20924000/trace-1750932222218210.json)

**Note: obtaining tracing output depends on #4406, but this PR is standalone and can be merged without waiting for #4406

r? `@RalfJung`

Author: GuillaumeGomez