This is needed to correctly handle the case, when we have the same java
class in common and platform module. In this scenario we have two
different classes on frontend (because symbol providers are not shared)
and completely different enhanced function in scopes of those classes,
but exactly one IrClass for those classes, which is cached during
conversion of common module together with cache of its fake overrides.
So using FirDeclaration as a key to FO cache leads to the problem, when
we can not find cached value for platform module, because it has different
fir declarations for the same real decalration
^KT-58030 Fixed
Dmitriy Novozhilov
15dfe6c750