refactor(codegen): accept SymbolTable instead of Mangler

[danbulant]

It seems to be that the easiest way to rename variables is to use rename_symbol from SymbolTable and to let it be applied during codegen - this is what Mangler does.

This PR changes Codegen to accept (any) SymbolTable instead of just Mangler itself, and for Mangler build output to be a new SymbolTable, after consuming itself (which makes it clear at the type level if a Mangler has been built or not).

This also moves the few symbol table helper methods from Mangler to SymbolTable itself, and adds an example of Mangler use to it's documentation.

Codegen dependencies now include semantic (which was transient by mangler before). It's dependency on Mangler could be removed, though I've left it to allow easy linking of docs (with_symbol_table points users to Mangler, hopefully helps with migration?)

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[codspeed-hq]

CodSpeed Performance Report

Merging #8829 will not alter performance

_{Comparing danbulant:main (26840a8) with main (831928d)}

Summary

✅ 33 untouched benchmarks