[FIR] Rewrite redeclaration checks

#KT-60124 Fixed
#KT-60573 Fixed

compiler/testData/diagnostics/tests/resolve/overloadConflicts/withVariance.fir.kt

@@ -1,9 +0,0 @@
-object X1
-object X2
-
-class A<T>
-
-fun <T1> A<T1>.foo() = X1
-fun <T2> A<out T2>.foo() = X2
-
-fun <T> A<out T>.test() = <!OVERLOAD_RESOLUTION_AMBIGUITY!>foo<!>() // TODO fix constraint system

compiler/testData/diagnostics/tests/resolve/overloadConflicts/withVariance.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 object X1
 object X2