[FIR] Set status.isOverride for fake overrides

Even though SO may not be correct
overrides sometimes, it feels more
natural to treat fake overrides as...
well, "overrides". And without it
we'd need to make the code in
`FirOverrideChecker` less intuitive.

analysis/analysis-api/testData/components/scopeProvider/memberScope/enumClass.pretty.txt

@@ -1,6 +1,6 @@
 protected fun clone(): kotlin.Any
 
-operator fun compareTo(other: test.E): kotlin.Int
+override operator fun compareTo(other: test.E): kotlin.Int
 
 operator fun equals(other: kotlin.Any?): kotlin.Boolean
 
@@ -13,9 +13,9 @@ val name: kotlin.String
 
 val ordinal: kotlin.Int
 
-fun getDeclaringClass(): java.lang.Class<test.E!>!
+override fun getDeclaringClass(): java.lang.Class<test.E!>!
 
-fun finalize()
+override fun finalize()
 
 companion object