Refactored ConvertMemberToExtension to re-use original declaration instead of regenerating it by text

#KT-4920 Fixed

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

@@ -1,5 +1,5 @@
 // ERROR: Property must be initialized
 class Owner {
     var <caret>p: Int
-      get() { return 1 }
+        get() { return 1 }
 }