consider emitting system function signatures

[holic]

right now we just emit world function signatures (useful to generate world ABI), but would be nice to emit system function signatures

my use case right now is #1611, going from config to onchain and back

• from config, I can get systems and register their function signatures and the registration methods handle prefixing them for me (turning them from system function signature to world function signature)
• from onchain, I can get systems and their world function signatures, but not the underlying system function signatures (just selector) to recreate a "system config"

to solve for this and have a common "system" definition (whether derived from onchain state or derived from config + system contracts), my TS code has to duplicate contract logic and either add the world prefix (local system contracts -> world function signatures) or remove the world prefix (onchain world function signatures -> system definition)

our FunctionSignatures table is offchain only and is just a mapping between selector -> signature, so we could just add an extra emission there when registerFunctionSelector is called (currently have one for world signature, need one for system signature)

[holic]

done in #2392
dupe of #2382