Merge pull request #6943 from dotty-staging/reporting-docs-update

Update `reporting` docs

Author: nicolasstucki

docs/docs/contributing/debugging.md

@@ -84,10 +84,10 @@ assertPositioned(tree)
 But you can also do:
 
 ```scala
-assertPositioned(tree.reporting(t => t.show))
+assertPositioned(tree.reporting(s"Tree is: $result"))
 ```
 
-`(a: A).reporting(f: A => String): A` is defined on all types. Its job is to print a `String` produced by the argument function and return the value it is called on unchanged.
+`def (a: A) reporting(f: given WrappedResult[T] => String, p: Printer = Printers.default): A` is defined on all types. The function `f` can be written without the argument since the argument is `given`. The `result` variable is a part of the `WrapperResult` – a tiny framework powering the `reporting` function. Basically, whenever you are using `reporting` on an object `A`, you can use the `result: A` variable from this function and it will be equal to the object you are calling `reporting` on.
 
 ## Printing out trees after phases
 To print out the trees you are compiling after Frontend (scanner, parser, namer, typer) phase: