DFA: count null comparison as identity comparison #KT-16538 Fixed

+ minor parameter refactoring

compiler/testData/diagnostics/tests/smartCasts/equals.kt

@@ -0,0 +1,25 @@
+fun foo(x: String?) = x
+
+class Test
+
+class TestWithEquals {
+    override fun equals(other: Any?) = super.equals(other)
+}
+
+fun bar(i: Test?) {
+    if (i == null) foo(<!DEBUG_INFO_CONSTANT!>i<!>)
+}
+
+fun bar(i: TestWithEquals?) {
+    if (i == null) foo(<!DEBUG_INFO_CONSTANT!>i<!>)
+    if (null == i) foo(<!DEBUG_INFO_CONSTANT!>i<!>)
+    when (i) {
+        null -> foo(<!DEBUG_INFO_CONSTANT!>i<!>)
+    }
+}
+
+fun gav(i: TestWithEquals?, j: TestWithEquals?) {
+    if (j == null) {
+        if (i == <!DEBUG_INFO_CONSTANT!>j<!>) foo(<!DEBUG_INFO_CONSTANT!>i<!>)
+    }
+}

compiler/testData/diagnostics/tests/smartCasts/equals.txt

@@ -0,0 +1,20 @@
+package
+
+public fun bar(/*0*/ i: Test?): kotlin.Unit
+public fun bar(/*0*/ i: TestWithEquals?): kotlin.Unit
+public fun foo(/*0*/ x: kotlin.String?): kotlin.String?
+public fun gav(/*0*/ i: TestWithEquals?, /*1*/ j: TestWithEquals?): kotlin.Unit
+
+public final class Test {
+    public constructor Test()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class TestWithEquals {
+    public constructor TestWithEquals()
+    public open override /*1*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}