Do not report "unused receiver" on companion objects

So #KT-19560 Fixed

idea/src/org/jetbrains/kotlin/idea/inspections/UnusedReceiverParameterInspection.kt

@@ -50,6 +50,10 @@ class UnusedReceiverParameterInspection : AbstractKotlinInspection() {
                 val receiverTypeReference = callableDeclaration.receiverTypeReference
                 if (receiverTypeReference == null || receiverTypeReference.textRange.isEmpty) return
 
+                val context = receiverTypeReference.analyze()
+                val receiverType = context[BindingContext.TYPE, receiverTypeReference] ?: return
+                if (DescriptorUtils.isCompanionObject(receiverType.constructor.declarationDescriptor)) return
+
                 if (callableDeclaration.isOverridable() ||
                     callableDeclaration.hasModifier(KtTokens.OVERRIDE_KEYWORD) ||
                     callableDeclaration.hasModifier(KtTokens.OPERATOR_KEYWORD) ||

idea/testData/inspectionsLocal/unusedReceiverParameter/companionPure.kt

@@ -0,0 +1,13 @@
+// PROBLEM: none
+
+class Test {
+    companion object {
+
+    }
+}
+
+fun <caret>Test.Companion.foo() = 42
+
+fun main(args: Array<String>) {
+    Test.foo()
+}

idea/testData/inspectionsLocal/unusedReceiverParameter/object.kt

@@ -0,0 +1,8 @@
+object Test
+
+fun <caret>Test.foo() = 42
+
+fun main(args: Array<String>) {
+    val x = Test
+    x.foo()
+}

idea/testData/inspectionsLocal/unusedReceiverParameter/object.kt.after

@@ -0,0 +1,8 @@
+object Test
+
+fun foo() = 42
+
+fun main(args: Array<String>) {
+    val x = Test
+    foo()
+}

idea/tests/org/jetbrains/kotlin/idea/inspections/LocalInspectionTestGenerated.java

@@ -2327,12 +2327,24 @@ public class LocalInspectionTestGenerated extends AbstractLocalInspectionTest {
             doTest(fileName);
         }
 
+        @TestMetadata("companionPure.kt")
+        public void testCompanionPure() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/inspectionsLocal/unusedReceiverParameter/companionPure.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("infix.kt")
         public void testInfix() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("idea/testData/inspectionsLocal/unusedReceiverParameter/infix.kt");
             doTest(fileName);
         }
 
+        @TestMetadata("object.kt")
+        public void testObject() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/inspectionsLocal/unusedReceiverParameter/object.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("operator.kt")
         public void testOperator() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("idea/testData/inspectionsLocal/unusedReceiverParameter/operator.kt");