Create From Usage: Generate Unit-typed declaration if result is unused

#KT-5903 Fixed

idea/testData/quickfix/createFromUsage/createFunction/binaryOperations/afterPlusAssignOnUserType.kt

@@ -1,7 +1,7 @@
 // "Create function 'plusAssign' from usage" "true"
 
 class A<T>(val n: T) {
-    fun plusAssign(arg: T): Unit {
+    fun plusAssign(arg: T) {
         throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.
     }
 }

idea/testData/quickfix/createFromUsage/createFunction/call/afterUnitFun.kt

@@ -0,0 +1,9 @@
+// "Create function 'foo' from usage" "true"
+
+fun test() {
+    foo(2, "2")
+}
+
+fun foo(i: Int, s: String) {
+    throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.
+}

idea/testData/quickfix/createFromUsage/createFunction/call/afterUnresolvedSupertype.kt

@@ -2,7 +2,7 @@
 // ERROR: Unresolved reference: B
 
 class A: B {
-    fun foo(): Any {
+    fun foo() {
         throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.
     }
 

idea/testData/quickfix/createFromUsage/createFunction/call/beforeUnitFun.kt

@@ -0,0 +1,5 @@
+// "Create function 'foo' from usage" "true"
+
+fun test() {
+    <caret>foo(2, "2")
+}