Infer implied outlives from fn signature

[kirloo]

What does this PR do?

Closes #405
Closes #202

How does it work, what questions do you have?

I created a new function implied_outlives_for_fn which goes through input argument and output types for a function and produces a Wcs corresponding to the function's implied outlives bounds. When encountering a ref it creates a WhereClause::Outlives for the inner type and the outer lifetime. The function recurses to handle nested borrows. The final Wcs is included in the assumptions of check_fn.

I think the logic seems sound and all tests pass, but:

• I'm not sure if I'm handling the case of multiple type parameters correctly (e.g. &'a HashMap<&'b K,&'c V>)
• I'm not sure if I'm handling the Arc in Parameter::Lt correctly.
• I'm not sure about function names and file structure.

Some old tests had to be updated due to the new assumptions.

This is a second attempt at #407 after I messed up the history trying to merge test updates.

AI disclosure

• I used an AI tool for research, autocomplete, or in other minimal ways

[rustbot]

Thanks for contributing to formality! :)
A reviewer will take a look at your PR within a week or two. If not, come talk to us on https://rust-lang.zulipchat.com/#narrow/channel/402470-t-types.2Fformality

[kirloo]

@nikomatsakis Now everything is in judgment functions

[nikomatsakis]

I guess I got a suggestion wrong @kirloo

 Error:   --> /home/runner/work/a-mir-formality/a-mir-formality/crates/formality-rust/src/check/implied_bounds.rs:40:1
   |
24 |     ) => Wcs {
   |              - the nearest open delimiter
...
32 |         )
   |         - missing open `(` for this delimiter
...
40 | }
   | ^ unexpected closing delimiter

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.