When there are multiple implementors for the same trait that is present
in an unmet binding, modify the E0277 error to refer to the parent
obligation and verify whether borrowing the argument being passed in
would satisfy the unmet bound. If it would, suggest it.
When a trait bound is not met and restricting a type parameter would
make the restriction hold, use a structured suggestion pointing at an
appropriate place (type param in param list or `where` clause).
Account for opaque parameters where instead of suggesting extending
the `where` clause, we suggest appending the new restriction:
`fn foo(impl Trait + UnmetTrait)`.
This commit updates the test output for the updated NLL compare mode
that uses `-Z borrowck=migrate` rather than `-Z borrowck=mir`. The
previous commit changes `compiletest` and this commit only updates
`.nll.stderr` files.
