- Dependency symbol providers contained a lot of useless
`FirExtensionSyntheticFunctionInterfaceProvider`s, because such a
provider only generates function classes from compiler plugins. If
there aren't any such `FunctionTypeKind`s in the session, there is no
need to even add the provider.
- `FirExtensionSyntheticFunctionInterfaceProvider`s that are added to
the list of dependency providers despite this optimization will now be
combined in `LLFirCombinedSyntheticFunctionSymbolProvider`. It checks
`ClassId` heuristics once, which is more efficient than checking them
in every provider separately.