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

#KT-4920 Fixed

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

@@ -0,0 +1,8 @@
+class Foo
+{
+    /**
+     * Doc
+     */
+    public val <caret>count: Int
+        get() = 1
+}