swift234

IRGen: Set up LinkEntities for protocol witness tables.

We need to handle three cases:

- If a protocol conformance has no associated types, or the associated type witnesses all have statically resolvable metadata, we can expose a *direct* witness table symbol.
- If a protocol conformance has associated types with runtime-instantiated metadata, we need to gate the witness table behind a *lazy* initializer function to fill in the metadata fields.
- If a protocol conformance has associated types where the type or one of its conformances are *dependent* on its parent's generic parameters, we need to instantiate multiple witness tables at runtime.

Swift SVN r6805