Fix the first example under "Parameter Types of Function Values"

The example had two issues:
1. It used `f` both as the name of the method and the argument. While it compiled, it seemed unnecessarily confusing to overload that name. So I changed the name of the function argument to +f2+.
2. The example failed to compile because it passed +String+ and +String => Int+ arguments. I fixed the example and added another one example for +Int+ and +Int => Int+ arguments.

Author: deanwampler

docs/docs/reference/changed-features/overload-resolution.md

@@ -52,9 +52,10 @@ that the remaining parameters suffice for picking a variant of the overloaded fu
 For example, the following code compiles in Dotty, while it results in an
 missing parameter type error in Scala2:
 ```scala
-def f(x: Int, f: Int => Int) = f(x)
-def f(x: String, f: String => String) = f(x)
-f("a", _.length)
+def f(x: Int, f2: Int => Int) = f2(x)
+def f(x: String, f2: String => String) = f2(x)
+f("a", _.toUpperCase)
+f(2, _ * 2)
 ```
 To make this work, the rules for overloading resolution in section 6.23.3 of the SLS are modified
 as follows: