doc: make minor improvements to fs.realpath() docs

Make canonical vs. unique text more precise and eliminate quotation
marks. Remove repeated text from fs.realpathSync(), linking to
fs.realpath() instead.

PR-URL: #20953
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/fs.md

@@ -2491,7 +2491,7 @@ changes:
Asynchronously computes the canonical pathname by resolving `.`, `..` and
symbolic links.

Note that "canonical" does not mean "unique": hard links and bind mounts can
A canonical pathname is not necessarily unique. Hard links and bind mounts can
expose a file system entity through many pathnames.

This function behaves like realpath(3), with some exceptions:
@@ -2566,26 +2566,7 @@ changes:
  * `encoding` {string} **Default:** `'utf8'`
* Returns: {string|Buffer}

Synchronously computes the canonical pathname by resolving `.`, `..` and
symbolic links.

Note that "canonical" does not mean "unique": hard links and bind mounts can
expose a file system entity through many pathnames.

This function behaves like realpath(3), with some exceptions:

1. No case conversion is performed on case-insensitive file systems.

2. The maximum number of symbolic links is platform-independent and generally
   (much) higher than what the native realpath(3) implementation supports.

The optional `options` argument can be a string specifying an encoding, or an
object with an `encoding` property specifying the character encoding to use for
the returned value. If the `encoding` is set to `'buffer'`, the path returned
will be passed as a `Buffer` object.

If `path` resolves to a socket or a pipe, the function will return a system
dependent name for that object.
Synchronous version of [`fs.realpath()`][]. Returns the resolved pathname.

## fs.realpathSync.native(path[, options])
<!-- YAML
@@ -4516,6 +4497,7 @@ the file contents.
[`fs.read()`]: #fs_fs_read_fd_buffer_offset_length_position_callback
[`fs.readFile()`]: #fs_fs_readfile_path_options_callback
[`fs.readFileSync()`]: #fs_fs_readfilesync_path_options
[`fs.realpath()`]: #fs_fs_realpath_path_options_callback
[`fs.rmdir()`]: #fs_fs_rmdir_path_callback
[`fs.stat()`]: #fs_fs_stat_path_callback
[`fs.utimes()`]: #fs_fs_utimes_path_atime_mtime_callback