GH-127381: pathlib ABCs: remove `PathBase.resolve()` and `absolute()` (#127707)

Remove our implementation of POSIX path resolution in `PathBase.resolve()`.
This functionality is rather fragile and isn't necessary in most cases. It
depends on `PathBase.stat()`, which we're looking to remove.

Also remove `PathBase.absolute()`. Many legitimate virtual filesystems lack
the notion of a 'current directory', so it's wrong to include in the basic
interface.