[red-knot] Internal refactoring of visibility constraints API (#15913)

This extracts some pure refactoring noise from
https://github.com/astral-sh/ruff/pull/15861. This changes the API for
creating and evaluating visibility constraints, but does not change how
they are respresented internally. There should be no behavioral or
performance changes in this PR.

Changes:

- Hide the internal representation isn't changed, so that we can make
changes to it in #15861.
- Add a separate builder type for visibility constraints. (With TDDs, we
will have some additional builder state that we can throw away once
we're done constructing.)
- Remove a layer of helper methods from `UseDefMapBuilder`, making
`SemanticIndexBuilder` responsible for constructing whatever visibility
constraints it needs.

crates/red_knot_python_semantic/src/semantic_index.rs

@@ -32,7 +32,7 @@ mod use_def;
 
 pub(crate) use self::use_def::{
     BindingWithConstraints, BindingWithConstraintsIterator, DeclarationWithConstraint,
-    DeclarationsIterator, ScopedVisibilityConstraintId,
+    DeclarationsIterator,
 };
 
 type SymbolMap = hashbrown::HashMap<ScopedSymbolId, (), FxBuildHasher>;