refactor ConvertFunctionToPropertyIntention and fix 'Convert function to property shouldn't insert explicit type if it was inferred previously' (#1011)

Fixes #KT-14820

idea/testData/intentions/convertFunctionToProperty/comments.kt.after

@@ -0,0 +1,9 @@
+annotation class X(val s: String)
+
+// 1
+@X("") // 2
+/* 3 */ val foo<caret>: String
+    get() {
+        // 4
+        return ""
+    }