[red-knot] Support TypeGuard and TypeIs

[InSyncWithFoo]

Summary

Part of #13694.

This PR's description is currently empty. See this comment for a list of unresolved major issues.

Test Plan

Markdown tests.

[MichaReiser]

It seems that the two types are exactly identical except for the name. Could we use a shared type (similar to Class) or make this type only thin wrapper types around a shared type? It would avoid the need for a macro

[InSyncWithFoo]

I started with that, but the various match/case function ended up quite unreadable, not to mention the subtle differences (e.g., TypeGuard[] is covariant, but TypeIs[] is invariant). All in all, I think the current approach is the best, despite being a little bit non-DRY.

[InSyncWithFoo]

This PR is incomplete (hence the empty description). Some major issues (all reflected in tests):

• Invalid definitions are supposed to be reported.
  I thought the logic could be added to .infer_function_definition(), but calling .infer_type_expression()/.infer_type_expression_no_store() there (on returns) leads to panic.

• if b where b is a bound guard is not recognized correctly.
  .evaluate_expr_name() needs some changes. However, I'm not sure if this approach scales, since b might not be a name.

• TypeGuard[]-based constraints should overrule all other constraints
  I have yet to find out a way to do this. It seems that constraints are considered always invertible and compatible with one another.

[MichaReiser]

I'm not sure if it's possible or reasonable here but I found many very specific mdtests much more helpful when debugging regression than a few tests that have many unrelated assertions.

There are also fewer trade-offs when using smaller tests compared to Ruff because it doesn't require you to create a new file. A single header is enough to create an isolated test.

[InSyncWithFoo]

Aren't all of these about function arity? I think this test is pretty small already, unless you mean the second file below (which is for subtype relation in TypeIs functions)?

[MichaReiser]

I think this PR has become stale or do you plan on continue working on this PR?

[InSyncWithFoo]

@MichaReiser I'm awaiting @carljm's reply at #117. In the meanwhile, I think I can at least split the working TypeIs parts into a separate PR; I'll do that next week.

[MichaReiser]

Thanks for the update :) I just went through some older PRs and it wasn't clear to me what we're waiting on for this one.

[carljm]

@InSyncWithFoo sorry I lost track of that! Replied now, let me know if you have other questions. Thanks for your work on this, and sorry we let it get stale!

[InSyncWithFoo]

Opened #18294 as a replacement for this one, since rebasing this would take too much effort.