FIR checker: fix positions of type mismatch on overrides

To handle implicit return types, those should be reported on
declarations with return type positioning strategy, instead of
return type itself.

compiler/testData/diagnostics/tests/CovariantOverrideType.fir.kt

@@ -1,26 +0,0 @@
-interface A<H> {
-    fun foo() : Int = 1
-    fun foo2() : Int = 1
-    fun foo1() : Int = 1
-    val a : Int
-    val a1 : Int
-    val g : Iterator<H>
-
-    fun <T> g() : T
-    fun <T> g1() : T
-}
-
-abstract class B<H>() : A<H> {
-    override fun foo() {
-    }
-    override fun foo2() : <!RETURN_TYPE_MISMATCH_ON_OVERRIDE!>Unit<!> {
-    }
-
-    override val a : <!PROPERTY_TYPE_MISMATCH_ON_OVERRIDE!>Double<!> = 1.toDouble()
-    override val a1 = 1.toDouble()
-
-    abstract override fun <X> g() : <!RETURN_TYPE_MISMATCH_ON_OVERRIDE!>Int<!>
-    abstract override fun <X> g1() : <!RETURN_TYPE_MISMATCH_ON_OVERRIDE!>List<X><!>
-
-    abstract override val g : <!PROPERTY_TYPE_MISMATCH_ON_OVERRIDE!>Iterator<Int><!>
-}

compiler/testData/diagnostics/tests/CovariantOverrideType.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 interface A<H> {
     fun foo() : Int = 1
     fun foo2() : Int = 1

compiler/testData/diagnostics/tests/delegatedProperty/delegatedPropertyOverridedInTraitTypeMismatch.fir.kt

@@ -1,21 +0,0 @@
-// !DIAGNOSTICS: -UNUSED_PARAMETER
-
-import kotlin.reflect.KProperty
-
-interface A {
-    val prop: Int
-}
-
-class AImpl: A  {
-    override val prop by Delegate()
-}
-
-fun foo() {
-    AImpl().prop
-}
-
-class Delegate {
-    operator fun getValue(t: Any?, p: KProperty<*>): <!PROPERTY_TYPE_MISMATCH_ON_OVERRIDE!>String<!> {
-        return ""
-    }
-}

compiler/testData/diagnostics/tests/delegatedProperty/delegatedPropertyOverridedInTraitTypeMismatch.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
 import kotlin.reflect.KProperty