pathlib ABCs: Require one or more initialiser arguments (#113885)

pathlib ABCs: Require one or more initialiser arguments (#113885)

Refuse to guess what a user means when they initialise a pathlib ABC
without any positional arguments. In mainline pathlib it's normalised to
`.`, but in the ABCs this guess isn't appropriate; for example, the path
type may not represent the current directory as `.`, or may have no concept
of a "current directory" at all.