FIR2IR: populate overriddenSymbols for overriding functions

#KT-38416 Fixed

compiler/testData/ir/irText/declarations/localClassWithOverrides.fir.txt

@@ -41,6 +41,8 @@ FILE fqName:<root> fileName:/localClassWithOverrides.kt
             DELEGATING_CONSTRUCTOR_CALL 'public constructor <init> () [primary] declared in <root>.outer.ALocal'
             INSTANCE_INITIALIZER_CALL classDescriptor='CLASS CLASS name:Local modality:FINAL visibility:local superTypes:[<root>.outer.ALocal]'
         FUN name:afun visibility:public modality:FINAL <> ($this:<root>.outer.Local) returnType:kotlin.Unit
+          overridden:
+            public abstract fun afun (): kotlin.Unit declared in <root>.outer.ALocal
           $this: VALUE_PARAMETER name:<this> type:<root>.outer.Local
           BLOCK_BODY
         PROPERTY name:aval visibility:public modality:FINAL [val]

compiler/testData/ir/irText/declarations/multiplatform/expectClassInherited.fir.txt

@@ -74,6 +74,8 @@ FILE fqName:<root> fileName:/expectClassInherited.kt
         DELEGATING_CONSTRUCTOR_CALL 'protected constructor <init> () [primary] declared in <root>.A'
         INSTANCE_INITIALIZER_CALL classDescriptor='CLASS CLASS name:B modality:OPEN visibility:public superTypes:[<root>.A]'
     FUN name:foo visibility:public modality:OPEN <> ($this:<root>.B) returnType:kotlin.Unit
+      overridden:
+        public abstract fun foo (): kotlin.Unit declared in <root>.A
       $this: VALUE_PARAMETER name:<this> type:<root>.B
       BLOCK_BODY
     FUN name:bar visibility:public modality:OPEN <> ($this:<root>.B, s:kotlin.String) returnType:kotlin.Unit