nightly-2024-07-28: feat: Remove 'comptime or separate crate' restriction on comptime cod…

…e (#5609)

# Description

## Problem\*

Resolves <none, this is a bonus>

## Summary\*

Removes the restriction that comptime code can only call into other
comptime code or code in a separate crate. This is possible now that
functions can be lazily resolved in the interpreter.

This means we no longer need hacky solutions like "comptime impl" on
trait impls. `comptime` itself also gets simplified from its previous
two meanings of "run this at comptime" and "make this visible to other
comptime code" to just "run this at comptime."

## Additional Context

I've also snuck in a sneaky ordering change where we run annotations on
traits before annotations on structs. Function annotations are still run
last.

## Documentation\*

Check one:
- [ ] No documentation needed.
- [ ] Documentation included in this PR.
- [x] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.