Fixed keywords after 'this@' completion + fixed implementation of JetExpressionWithLabel.getLabelName()

idea/idea-completion/testData/handlers/smart/QualifiedThisKeywordName1.kt

@@ -4,5 +4,5 @@ class `this` {
     }
 }
 
-// ELEMENT: "this@this"
+// ELEMENT: "this@`this`"
 

idea/idea-completion/testData/handlers/smart/QualifiedThisKeywordName1.kt.after

@@ -1,8 +1,8 @@
 class `this` {
     fun String.foo(){
-        val foo: `this` = this@this<caret>
+        val foo: `this` = this@`this`<caret>
     }
 }
 
-// ELEMENT: "this@this"
+// ELEMENT: "this@`this`"
 

idea/idea-completion/testData/handlers/smart/QualifiedThisKeywordName2.kt

@@ -9,4 +9,4 @@ fun foo(){
             })
 }
 
-// ELEMENT: this@fun
+// ELEMENT: this@`fun`

idea/idea-completion/testData/handlers/smart/QualifiedThisKeywordName2.kt.after

@@ -4,9 +4,9 @@ fun bar(handler: Int.() -> Unit){}
 fun foo(){
     `fun`({
                 bar({
-                            val s: String = this@fun<caret>
+                            val s: String = this@`fun`<caret>
                         })
             })
 }
 
-// ELEMENT: this@fun
+// ELEMENT: this@`fun`

idea/idea-completion/testData/keywords/ReturnKeywordName.kt

@@ -0,0 +1,14 @@
+fun foo() {
+    `fun` {
+        `val`({ ret<caret> })
+    }
+}
+
+inline fun `fun`(handler: () -> Unit){}
+inline fun `val`(handler: () -> Unit){}
+
+// INVOCATION_COUNT: 1
+// EXIST: { lookupString: "return", itemText: "return", tailText: null, attributes: "bold" }
+// EXIST: { lookupString: "return@`fun`", itemText: "return", tailText: "@`fun`", attributes: "bold" }
+// EXIST: { lookupString: "return@`val`", itemText: "return", tailText: "@`val`", attributes: "bold" }
+// NOTHING_ELSE: true