Smaller range + refactoring of ConvertMemberToExtension

idea/testData/intentions/declarations/convertMemberToExtension/funcitonNoName.kt

@@ -1,3 +1,4 @@
+// IS_APPLICABLE: false
 // ERROR: Function declaration must have a name
 class Owner {
   fun <caret>() {}

idea/testData/intentions/declarations/convertMemberToExtension/funcitonNoName.kt.after

@@ -1,6 +0,0 @@
-// ERROR: Function declaration must have a name
-class Owner {
-}
-
-fun Owner.() {
-}