rustfix: Autofix try! macro in edition lint to use `?` operator

[tesuji]

Now try! macro has been deprecated in #62672. I think it's time to automatically
fix try!(expr) to expr? in edition lint.

[tesuji]

@rustbot modify labels: A-diagnostics A-edition-2018-lints A-lint A-suggestion-diagnostics T-compiler

[jugglerchris]

I've got code with a load of r#try so this one's bugging me. :-)

I'm interested in working on it if no-one else is. I haven't worked on rustc so there'll be some learning for me to do first.

[taiki-e]

FYI: rustfmt already provides a feature to replace try!(expr) to expr?.: https://github.com/rust-lang/rustfmt/blob/master/Configurations.md#use_try_shorthand

[Centril]

iirc we took a fairly explicit decision to migrate to r#try!(...) because migrating to ? can break code. And we cannot be sure everyone has migrated to 2018. cc @rust-lang/lang

[tesuji]

But this is edition lint for anyone want to migrate from 2015 to 2018 edition.

[jugglerchris]

@Centril under what circumstances can ? break code compared to r#try!(...)?