These refer to external functions and function signatures declared in
the preamble. Since we're already using the type names 'Signature' and
'Function', these entity references don't folow the usual EntityData /
Entity naming convention.
Require this trait on the value type stored in an EntityMap to 'unlock' the
methods intended for primary entity maps that are allowed to create references
with the 'push method.
This prevents accidentally depending on these methods in secondary maps.
- Add a ir::jumptable module with a JumpTableData struct representing the vector
of destinations.
- Add an entity map of jump tables to the Function.
- Parse and write jump tables in the function preamble.
- Rewrite EBB references in jumptables after parsing.
