add `nonpoison::mutex` implementation

Adds the equivalent `nonpoison` types to the `poison::mutex` module.
These types and implementations are gated under the `nonpoison_mutex`
feature gate.

Also blesses the ui tests that now have a name conflicts (because these
types no longer have unique names). The full path distinguishes the
different types.

Co-authored-by: Aandreba <aandreba@gmail.com>
Co-authored-by: Trevor Gross <tmgross@umich.edu>