rev-parse: handle --end-of-options

We taught rev-list a new way to separate options from revisions in
19e8789b23 (revision: allow --end-of-options to end option parsing,
2019-08-06), but rev-parse uses its own parser. It should know about
--end-of-options not only for consistency, but because it may be
presented with similarly ambiguous cases. E.g., if a caller does:

  git rev-parse "$rev" -- "$path"

to parse an untrusted input, then it will get confused if $rev contains
an option-like string like "--local-env-vars". Or even "--not-real",
which we'd keep as an option to pass along to rev-list.

Or even more importantly:

  git rev-parse --verify "$rev"

can be confused by options, even though its purpose is safely parsing
untrusted input. On the plus side, it will always fail the --verify
part, as it will not have parsed a revision, so the caller will
generally "fail closed" rather than continue to use the untrusted
string. But it will still trigger whatever option was in "$rev"; this
should be mostly harmless, since rev-parse options are all read-only,
but I didn't carefully audit all paths.

This patch lets callers write:

  git rev-parse --end-of-options "$rev" -- "$path"

and:

  git rev-parse --verify --end-of-options "$rev"

which will both treat "$rev" always as a revision parameter. The latter
is a bit clunky. It would be nicer if we had defined "--verify" to
require that its next argument be the revision. But we have not
historically done so, and:

  git rev-parse --verify -q "$rev"

does currently work. I added a test here to confirm that we didn't break
that.

A few implementation notes:

 - We don't document --end-of-options explicitly in commands, but rather
   in gitcli(7). So I didn't give it its own section in git-rev-parse(1).
   But I did call it out specifically in the --verify section, and
   include it in the examples, which should show best practices.

 - We don't have to re-indent the main option-parsing block, because we
   can combine our "did we see end of options" check with "does it start
   with a dash". The exception is the pre-setup options, which need
   their own block.

 - We do however have to pull the "--" parsing out of the "does it start
   with dash" block, because we want to parse it even if we've seen
   --end-of-options.

 - We'll leave "--end-of-options" in the output. This is probably not
   technically necessary, as a careful caller will do:

     git rev-parse --end-of-options $revs -- $paths

   and anything in $revs will be resolved to an object id. However, it
   does help a slightly less careful caller like:

     git rev-parse --end-of-options $revs_or_paths

   where a path "--foo" will remain in the output as long as it also
   exists on disk. In that case, it's helpful to retain --end-of-options
   to get passed along to rev-list, s it would otherwise see just
   "--foo".

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

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