Introduce inspection: "Setter backing field should be assigned"

#KT-20273 Fixed

idea/testData/inspectionsLocal/setterBackingFieldAssignment/.inspection

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

idea/testData/inspectionsLocal/setterBackingFieldAssignment/assignment.kt

@@ -0,0 +1,10 @@
+// PROBLEM: none
+class Test {
+    var foo: Int = 1
+        <caret>set(value) {
+            bar()
+            field = value
+        }
+
+    fun bar() {}
+}

idea/testData/inspectionsLocal/setterBackingFieldAssignment/decrement.kt

@@ -0,0 +1,7 @@
+// PROBLEM: none
+class Test {
+    var foo: Int = 10
+        <caret>set(value) {
+            field--
+        }
+}

idea/testData/inspectionsLocal/setterBackingFieldAssignment/decrement2.kt

@@ -0,0 +1,7 @@
+// PROBLEM: none
+class Test {
+    var foo: Int = 10
+        <caret>set(value) {
+            --field
+        }
+}

idea/testData/inspectionsLocal/setterBackingFieldAssignment/divAssign.kt

@@ -0,0 +1,7 @@
+// PROBLEM: none
+class Test {
+    var foo: Int = 10
+        <caret>set(value) {
+            field /= value
+        }
+}

idea/testData/inspectionsLocal/setterBackingFieldAssignment/functionCallWithSetterParam.kt

@@ -0,0 +1,9 @@
+// PROBLEM: none
+class Test {
+    var foo: Int = 10
+        <caret>set(value) {
+            bar(value)
+        }
+
+    fun bar(value: Int) {}
+}

idea/testData/inspectionsLocal/setterBackingFieldAssignment/increment.kt

@@ -0,0 +1,7 @@
+// PROBLEM: none
+class Test {
+    var foo: Int = 10
+        <caret>set(value) {
+            field++
+        }
+}

idea/testData/inspectionsLocal/setterBackingFieldAssignment/increment2.kt

@@ -0,0 +1,7 @@
+// PROBLEM: none
+class Test {
+    var foo: Int = 10
+        <caret>set(value) {
+            ++field
+        }
+}

idea/testData/inspectionsLocal/setterBackingFieldAssignment/minusAssign.kt

@@ -0,0 +1,7 @@
+// PROBLEM: none
+class Test {
+    var foo: Int = 10
+        <caret>set(value) {
+            field -= value
+        }
+}

idea/testData/inspectionsLocal/setterBackingFieldAssignment/modAssign.kt

@@ -0,0 +1,7 @@
+// PROBLEM: none
+class Test {
+    var foo: Int = 10
+        <caret>set(value) {
+            field %= value
+        }
+}

idea/testData/inspectionsLocal/setterBackingFieldAssignment/noAssignment.kt

@@ -0,0 +1,5 @@
+class Test {
+    var foo: Int = 1
+        <caret>set(value) {
+        }
+}

idea/testData/inspectionsLocal/setterBackingFieldAssignment/noAssignment.kt.after

@@ -0,0 +1,6 @@
+class Test {
+    var foo: Int = 1
+        set(value) {
+            field = value
+        }
+}

idea/testData/inspectionsLocal/setterBackingFieldAssignment/noAssignment2.kt

@@ -0,0 +1,8 @@
+class Test {
+    var foo: Int = 1
+        <caret>set(value) {
+            bar(field)
+        }
+
+    fun bar(i: Int) {}
+}

idea/testData/inspectionsLocal/setterBackingFieldAssignment/noAssignment2.kt.after

@@ -0,0 +1,9 @@
+class Test {
+    var foo: Int = 1
+        set(value) {
+            bar(field)
+            field = value
+        }
+
+    fun bar(i: Int) {}
+}

idea/testData/inspectionsLocal/setterBackingFieldAssignment/noBackingField.kt

@@ -0,0 +1,7 @@
+// PROBLEM: none
+class Test {
+    var foo: Int
+        get() = 1
+        <caret>set(value) {
+        }
+}

idea/testData/inspectionsLocal/setterBackingFieldAssignment/plusAssign.kt

@@ -0,0 +1,7 @@
+// PROBLEM: none
+class Test {
+    var foo: Int = 10
+        <caret>set(value) {
+            field += value
+        }
+}

idea/testData/inspectionsLocal/setterBackingFieldAssignment/timesAssign.kt

@@ -0,0 +1,7 @@
+// PROBLEM: none
+class Test {
+    var foo: Int = 10
+        <caret>set(value) {
+            field *= value
+        }
+}