Fix JetType.equals(): flexible types are not equal to non-flexible ones, when we store them in a HashSet

compiler/testData/diagnostics/tests/inference/immutableArrayList.kt

@@ -0,0 +1,17 @@
+// FILE: p/J.java
+package p;
+
+public interface J {
+    public interface Super<T> {}
+    public interface Sub<T> extends Super<T> {}
+}
+
+// FILE: k.kt
+
+import p.J.*
+
+class Foo<T>: Sub<T> {
+    fun foo(): Super<T> {
+        return <!TYPE_INFERENCE_NO_INFORMATION_FOR_PARAMETER!>Foo<!>()
+    }
+}

compiler/testData/diagnostics/tests/inference/immutableArrayList.txt

@@ -0,0 +1,9 @@
+package
+
+internal final class Foo</*0*/ T> : p.J.Sub<T> {
+    public constructor Foo</*0*/ T>()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    internal final fun foo(): p.J.Super<T>
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/platformTypes/commonSupertype/typeOfElvis.kt

@@ -0,0 +1,20 @@
+// FILE: p/J.java
+
+package p;
+
+public class J {
+    public static J j() { return null; }
+}
+
+// FILE: k.kt
+
+import p.*
+
+fun foo(): J? = null
+
+fun main(args: Array<String>) {
+    val v = foo() ?: J.j()
+    if (v != null) {
+
+    }
+}

compiler/testData/diagnostics/tests/platformTypes/commonSupertype/typeOfElvis.txt

@@ -0,0 +1,4 @@
+package
+
+internal fun foo(): p.J?
+internal fun main(/*0*/ args: kotlin.Array<kotlin.String>): kotlin.Unit