[red-knot] Don't use separate ID types for each alist (#16415)

Regardless of whether #16408 and #16311 pan out, this part is worth
pulling out as a separate PR.

Before, you had to define a new `IndexVec` index type for each type of
association list you wanted to create. Now there's a single index type
that's internal to the alist implementation, and you use `List<K, V>` to
store a handle to a particular list.

This also adds some property tests for the alist implementation.

crates/red_knot_python_semantic/src/lib.rs

@@ -14,6 +14,7 @@ pub use semantic_model::{HasType, SemanticModel};
 pub mod ast_node_ref;
 mod db;
 pub mod lint;
+pub(crate) mod list;
 mod module_name;
 mod module_resolver;
 mod node_key;