KT-7756 Completion of "return null", "return true" and "return false"

#KT-7756 Fixed

idea/idea-completion/testData/handlers/keywords/ReturnNull.kt

@@ -0,0 +1,5 @@
+fun foo(): String? {
+    ret<caret>
+}
+
+// ELEMENT: "return null"

idea/idea-completion/testData/handlers/keywords/ReturnNull.kt.after

@@ -0,0 +1,5 @@
+fun foo(): String? {
+    return null<caret>
+}
+
+// ELEMENT: "return null"

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

@@ -0,0 +1,9 @@
+fun foo(): Boolean {
+    ret<caret>
+}
+
+// INVOCATION_COUNT: 1
+// EXIST: { lookupString: "return", itemText: "return", tailText: null, attributes: "bold" }
+// EXIST: { lookupString: "return true", itemText: "return true", tailText: null, attributes: "bold" }
+// EXIST: { lookupString: "return false", itemText: "return false", tailText: null, attributes: "bold" }
+// NOTHING_ELSE: true

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

@@ -0,0 +1,8 @@
+fun foo(): String {
+    ret<caret>
+}
+
+// INVOCATION_COUNT: 1
+// ABSENT: "return null"
+// ABSENT: "return true"
+// ABSENT: "return false"

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

@@ -0,0 +1,8 @@
+fun foo(): String? {
+    ret<caret>
+}
+
+// INVOCATION_COUNT: 1
+// EXIST: { lookupString: "return", itemText: "return", tailText: null, attributes: "bold" }
+// EXIST: { lookupString: "return null", itemText: "return null", tailText: null, attributes: "bold" }
+// NOTHING_ELSE: true

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

@@ -0,0 +1,10 @@
+fun foo(): Boolean? {
+    ret<caret>
+}
+
+// INVOCATION_COUNT: 1
+// EXIST: { lookupString: "return", itemText: "return", tailText: null, attributes: "bold" }
+// EXIST: { lookupString: "return null", itemText: "return null", tailText: null, attributes: "bold" }
+// EXIST: { lookupString: "return true", itemText: "return true", tailText: null, attributes: "bold" }
+// EXIST: { lookupString: "return false", itemText: "return false", tailText: null, attributes: "bold" }
+// NOTHING_ELSE: true

idea/idea-completion/testData/weighers/basic/ReturnBoolean.kt

@@ -0,0 +1,7 @@
+fun foo(): Boolean {
+    ret<caret>
+}
+
+// ORDER: return
+// ORDER: return false
+// ORDER: return true