Report a warning when comparing incompatible enums

I've put `isIncompatibleEnums` to TypeIntersector because I placed
all of its usages after all of the TypeIntersector::isIntersectionEmpty ones

^KT-28225 Fixed

compiler/testData/diagnostics/tests/enum/incompatibleEnumEntryClasses.kt

@@ -0,0 +1,90 @@
+interface I {
+    fun foo()
+}
+
+enum class E1 : I {
+    A {
+        override fun foo() {
+            <!EQUALITY_NOT_APPLICABLE!>this == E2.A<!>
+
+            val q = this
+            when (q) {
+                this -> {}
+                E1.A -> {}
+                E1.B -> {}
+                <!INCOMPATIBLE_TYPES!>E2.A<!> -> {}
+                <!INCOMPATIBLE_TYPES!>E2.B<!> -> {}
+                else -> {}
+            }
+        }
+    },
+    B {
+        override fun foo() {
+
+        }
+    }
+}
+
+enum class E2 : I {
+    A {
+        override fun foo() {
+
+        }
+    },
+    B {
+        override fun foo() {
+
+        }
+    }
+}
+
+fun foo1(e1: E1, e2: E2) {
+    <!INCOMPATIBLE_ENUM_COMPARISON!>e1 == e2<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON!>e1 != e2<!>
+
+    <!INCOMPATIBLE_ENUM_COMPARISON!>e1 == E2.A<!>
+    <!INCOMPATIBLE_ENUM_COMPARISON!>E1.B == e2<!>
+
+    <!INCOMPATIBLE_ENUM_COMPARISON!>E1.A == E2.B<!>
+
+    e1 == E1.A
+    E1.A == e1
+    e2 == E2.B
+    E2.B == e2
+}
+
+fun foo2(e1: E1, e2: E2) {
+    when (e1) {
+        E1.A -> {}
+        <!INCOMPATIBLE_ENUM_COMPARISON!>E2.A<!> -> {}
+        <!INCOMPATIBLE_ENUM_COMPARISON!>E2.B<!> -> {}
+        e1 -> {}
+        <!INCOMPATIBLE_ENUM_COMPARISON!>e2<!> -> {}
+        else -> {}
+    }
+}
+
+fun foo3(e1: Enum<E1>, e2: Enum<E2>, e: Enum<*>) {
+    e1 == e
+    e1 == e2
+
+    e1 == E1.A
+    e1 == E2.A
+
+    when (e1) {
+        e1 -> {}
+        e2 -> {}
+        e -> {}
+        E1.A -> {}
+        E2.A -> {}
+        else -> {}
+    }
+
+    when (e) {
+        e -> {}
+        e2 -> {}
+        E1.A -> {}
+        E2.A -> {}
+        else -> {}
+    }
+}