Simplify data class function generation and signature lookup code

- change prerequisites for generating equals/hashCode/toString in a data class:
  previously they were generated if the corresponding method is trivial (i.e.
  it comes from kotlin.Any), now we're generating it always unless it'll cause
  a JVM signature clash error (see KT-6206)
- use static KotlinBuiltIns.isXxx methods to compare types instead of checking
  against descriptors loaded from certain built-ins instance, this is quicker
  and more correct in environments where several built-ins are possible
- don't use isOrOverridesSynthesized, it's not relevant for
  equals/hashCode/toString because functions with these names are never
  synthesized

 #KT-6206 Fixed

compiler/testData/codegen/box/dataClasses/nonTrivialFinalMemberInSuperClass.kt

@@ -0,0 +1,20 @@
+// TODO: remove the suppression once data classes can have supertypes
+@file:Suppress("DATA_CLASS_CANNOT_HAVE_CLASS_SUPERTYPES")
+
+abstract class Base {
+    final override fun toString() = "OK"
+    final override fun hashCode() = 42
+    final override fun equals(other: Any?) = false
+}
+
+data class DataClass(val field: String) : Base()
+
+fun box(): String {
+    val d = DataClass("x")
+
+    if (d.toString() != "OK") return "Fail toString"
+    if (d.hashCode() != 42) return "Fail hashCode"
+    if (d.equals(d) != false) return "Fail equals"
+
+    return "OK"
+}

compiler/testData/codegen/box/dataClasses/nonTrivialMemberInSuperClass.kt

@@ -0,0 +1,21 @@
+// See KT-6206 Always generate hashCode() and equals() for data classes even if base classes have non-trivial analogs
+// TODO: remove the suppression once data classes can have supertypes
+@file:Suppress("DATA_CLASS_CANNOT_HAVE_CLASS_SUPERTYPES")
+
+abstract class Base {
+    override fun toString() = "Fail"
+    override fun hashCode() = -42
+    override fun equals(other: Any?) = false
+}
+
+data class DataClass(val field: String) : Base()
+
+fun box(): String {
+    val d = DataClass("x")
+
+    if (d.toString() != "DataClass(field=x)") return "Fail toString"
+    if (d.hashCode() != "x".hashCode()) return "Fail hashCode"
+    if (d.equals(d) == false) return "Fail equals"
+
+    return "OK"
+}