realpath: implement missing command-line arguments

[jfinkels]

GNU coreutils realpath v8.28 has the following arguments:

$ realpath --help
Usage: realpath [OPTION]... FILE...
Print the resolved absolute file name;
all but the last component must exist

  -e, --canonicalize-existing  all components of the path must exist
  -m, --canonicalize-missing   no path components need exist or be a directory
  -L, --logical                resolve '..' components before symlinks
  -P, --physical               resolve symlinks as encountered (default)
  -q, --quiet                  suppress most error messages
      --relative-to=DIR        print the resolved path relative to DIR
      --relative-base=DIR      print absolute paths unless paths below DIR
  -s, --strip, --no-symlinks   don't expand symlinks
  -z, --zero                   end each output line with NUL, not newline

      --help     display this help and exit
      --version  output version information and exit

GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
Full documentation at: <http://www.gnu.org/software/coreutils/realpath>
or available locally via: info '(coreutils) realpath invocation'

whereas the uutils version has only

$ ./target/debug/coreutils realpath -h
realpath 0.0.6
print the resolved path

USAGE:
    realpath [OPTION]... FILE...

FLAGS:
    -h, --help       Prints help information
    -q, --quiet      Do not print warnings for invalid paths
    -s, --strip      Only strip '.' and '..' components, but don't resolve symbolic links
    -V, --version    Prints version information
    -z, --zero       Separate output filenames with \0 rather than newline

ARGS:
    <files>...    

Specifically, it is missing options -e, -m, -L, --relative-to, and --relative-base.

[tertsdiepraam]

Actually, -L is implemented and -P is missing:

❯ exa --tree
.
├── a
│  ├── b
│  └── hello.txt
└── b.link -> a/b

GNU:

❯ realpath b.link/../hello.txt
/home/terts/Programming/coreutils/test_folder/a/hello.txt <-- inside a
❯ realpath -L b.link/../hello.txt
/home/terts/Programming/coreutils/test_folder/hello.txt   <-- outside a

Uutils:

❯ uu_realpath b.link/../hello.txt
/home/terts/Programming/coreutils/test_folder/hello.txt   <-- outside a

[jfinkels]

Pull request #2459 implemented -L and -P so the remaining options to be implemented are

  -e, --canonicalize-existing  all components of the path must exist
  -m, --canonicalize-missing   no path components need exist or be a directory
      --relative-to=DIR        print the resolved path relative to DIR
      --relative-base=DIR      print absolute paths unless paths below DIR

[jaggededgedjustice]

I'm working on adding the -e/-m option.

[niyaznigmatullin]

PR #3710 implemented --relative-to and --relative-base.

-e and -m were implemented before, I think this can be closed