swift234

[Fixit] Add a fixit for converting non-trailing closures to trailing closures.

Reminded by Ben's last commit of code completion, I noticed that some users
do not use trailing closures when helping migrating their code. To enhance the discoverability
of this feature, this fix helps users to convert non-trailing closures to trailing
closures. To ensure disambiguity after conversion, we check name conflict before adding
the note.