Add 'Covariant equals' inspection

#KT-29798 Fixed

idea/testData/inspectionsLocal/covariantEquals/.inspection

@@ -0,0 +1 @@
+org.jetbrains.kotlin.idea.inspections.KotlinCovariantEqualsInspection

idea/testData/inspectionsLocal/covariantEquals/basic.kt

@@ -0,0 +1,7 @@
+// PROBLEM: 'equals' should take 'Any?' as its argument
+// FIX: none
+class Foo {
+    fun <caret>equals(other: Foo?): Boolean {
+        return true
+    }
+}

idea/testData/inspectionsLocal/covariantEquals/hasOverriddenAnyEquals.kt

@@ -0,0 +1,10 @@
+// PROBLEM: none
+class Foo {
+    fun <caret>equals(other: Foo?): Boolean {
+        return true
+    }
+
+    override fun equals(other: Any?): Boolean {
+        return true
+    }
+}

idea/testData/inspectionsLocal/covariantEquals/inCompanion.kt

@@ -0,0 +1,8 @@
+// PROBLEM: none
+class F {
+    companion object {
+        fun <caret>equals(other: F?): Boolean {
+            return true
+        }
+    }
+}

idea/testData/inspectionsLocal/covariantEquals/inObject.kt

@@ -0,0 +1,7 @@
+// PROBLEM: 'equals' should take 'Any?' as its argument
+// FIX: none
+object F {
+    fun <caret>equals(other: F?): Boolean {
+        return true
+    }
+}

idea/testData/inspectionsLocal/covariantEquals/inObjectLiteral.kt

@@ -0,0 +1,9 @@
+// PROBLEM: 'equals' should take 'Any?' as its argument
+// FIX: none
+interface F
+
+val f = object : F {
+    fun <caret>equals(other: F?): Boolean {
+        return true
+    }
+}

idea/testData/inspectionsLocal/covariantEquals/local.kt

@@ -0,0 +1,9 @@
+// PROBLEM: none
+class Foo {
+    fun test() {
+        fun <caret>equals(other: Foo?): Boolean {
+            return true
+        }
+        equals(null)
+    }
+}

idea/testData/inspectionsLocal/covariantEquals/override.kt

@@ -0,0 +1,13 @@
+// PROBLEM: 'equals' should take 'Any?' as its argument
+// FIX: none
+open class Foo {
+    open fun equals(other: Foo?): Boolean {
+        return true
+    }
+}
+
+class Bar : Foo() {
+    override fun <caret>equals(other: Foo?): Boolean {
+        return true
+    }
+}

idea/testData/inspectionsLocal/covariantEquals/overrideAnyEquals.kt

@@ -0,0 +1,6 @@
+// PROBLEM: none
+class Foo {
+    override fun <caret>equals(other: Any?): Boolean {
+        return true
+    }
+}

idea/testData/inspectionsLocal/covariantEquals/topLevel.kt

@@ -0,0 +1,4 @@
+// PROBLEM: none
+fun <caret>equals(other: Any?): Boolean {
+    return true
+}

idea/testData/inspectionsLocal/covariantEquals/twoParameters.kt

@@ -0,0 +1,6 @@
+// PROBLEM: none
+class Foo {
+    fun <caret>equals(other: Foo?, other2: Foo?): Boolean {
+        return true
+    }
+}