Invocations of this macro instruct Rerast to replace the first expression/statement with the one
after the =>. For example replace!(5 => 6) says to replace all occurences of the literal 5 with
the literal 6.
Replaces a pattern with another pattern. A placeholder is required in order to specify the types
of the search and replacement pattern. Although they can be the same if you’re replacing a
pattern with another of the same type.
Replaces one type with another. This will not match trait bounds (e.g. in where clauses), since
they are not types. If you want to replace all references to a trait, use replace_trait_ref!
instead.