GH-127381: pathlib ABCs: remove `PathBase.samefile()` and rarer `is_*()` (#127709)

Remove `PathBase.samefile()`, which is fairly specific to the local FS, and
relies on `stat()`, which we're aiming to remove from `PathBase`.

Also remove `PathBase.is_mount()`, `is_junction()`, `is_block_device()`,
`is_char_device()`, `is_fifo()` and `is_socket()`. These rely on POSIX
file type numbers that we're aiming to remove from the `PathBase` API.