KT-1934 Check inherited signatures for compatibility

Overridden signatures should have compatible return types
(equal types for 'var').
Only relevant overrides should be taken into account.
Refactor inherited signatures check,
introduce a strategy interface for problem reporting.

compiler/testData/diagnostics/tests/override/clashesOnInheritance/unrelatedInherited.kt

@@ -0,0 +1,33 @@
+interface IA {
+    fun method(): String
+    val propVal: String
+    var propVar: String
+}
+
+interface IB1 : IA
+interface IB2 : IA
+
+interface IGA<T> {
+    fun method(): T
+    val propVal: T
+    var propVar: T
+}
+
+interface IGB1Str : IGA<String>
+interface IGB2Str : IGA<String>
+interface IGB3Int : IGA<Int>
+
+interface IGB4T<T> : IGA<T>
+interface IGB5T<T> : IGA<T>
+
+interface IC : IB1, IB2
+
+interface IGC1 : IGB1Str, IGB2Str
+
+interface IGC2 : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>IGB1Str, IGB3Int<!>
+
+interface IGC3<T> : IGB4T<T>, IGB5T<T>
+
+interface IGC4<T> : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>IGB4T<T>, IGB5T<String><!>
+
+interface IGC5 : IGB4T<String>, IGB5T<String>