Smarter `find_case` for `eq_file`

[epage]

Right now, its a default implementation

Ideally

• For Str, perform difference where applicable
  • Do we also need to do this for eval? Not sure if there is a difference

[mzabaluev]

Wouldn't it be nice to make case finders composable? Something like

use predicates::str::Diff as _;

predicate::path::eq_file(p).utf8().diff()

would not change how eval works, but would modify the case finder into what DifferencePredicate uses now.