SI-6613 Make Java enums work in FSC / REPL

We needed to hop from the enum's owner to its companion
module in an early phase of the compiler.

The enclosed test used to fail when this lookup returned
NoSymbol on the second run of the resident compiler when
triggered from `MixinTransformer`: the lookup didn't work
after the flatten info transform. This is related to the
fact that module classes are flattened into the enclosing
package, but module accessors remain in the enclosing class.