Almost all operations on Path are based on the components iterator in one form
or another to handle equivalent paths. The `Hash` implementations, however,
mistakenly just went straight to the underlying `OsStr`, causing these
equivalent paths to not get merged together.
This commit updates the `Hash` implementation to also be based on the iterator
which should ensure that if two paths are equal they hash to the same thing.
cc #29008, but doesn't close it
d2dd700891