Extract commonly used visitors to utils

[flip1995]

Both #3427 and #4386 implement a Visitor that walks an expression and searches for a return. This should be de-duplicated.

Maybe there are other Visitors in the Clippy code base, that also do similar things and can be extracted to utils.

Originally posted by @mikerite in #4386 (comment)

[phansch]

I don't really have any experience working with visitors, so I'd like to pick this up ✋

[phansch]

One problem I see is that one visitor works on ast::Expr to check for ast::ExprKind::Try but the second visitor is used in a LateContext which doesn't have access to the AST types anymore and can't check for Try. That would make it impossible to combine these two, no?

[flip1995]

Jop, that makes this impossible. Maybe the LatePass lint can be moved to an EarlyPass?