This currently changes builtin realpath with the "-s" option:
builtin realpath -s ///tmp
previously would print "///tmp", now it prints "/tmp".
The only thing "allow_leading_double_slashes" does is allow *two*
slashes.
This is important for `path match`, to be introduced in #8265.
This used the *logical* $PWD, but realpath would operate on the
physical $PWD if given ".", even with -s. This makes this test fail if the $PWD is
logically different from physical.
Taken from GNU realpath, this one makes realpath not resolve symlinks.
It still makes paths absolute and handles duplicate and trailing
slashes.
(useful in fish_add_path)
I'm gonna add more tests to this and I don't want to touch the old stuff.
Notice that this needs to have the output of the complete_directories
test adjusted because this one now runs later.
That's something we should take into account in future.
