Hi,

I'm getting a kind of undefined behavior where parenthesis seem handled in a strange way. On display, it has a conflict between parenthesis of the option, and nested parenthesis within a metavar.

## Reproduction script

```
import argparse

def main():
    parser = argparse.ArgumentParser()

    group = parser.add_mutually_exclusive_group(required=True)

    group.add_argument("-p", "--path", metavar="/var/www/html", 
            help="DocumentRoot path")
    group.add_argument("-r", "--reverse", metavar="http)s(://Host:Port",
            help="Reverse proxy address")

    parser.add_argument("--last-args")
    return parser.parse_args()

main()
```

## Output of help menu
```
usage: crash.py [-h] (-p /var/www/html | -r http)s://Host:Port [--last-args LAST_ARGS]
```

## Expected behavior
```
usage: crash.py [-h] (-p /var/www/html | -r http)s(://Host:Port) [--last-args LAST_ARGS]
```

I confirm this happens on all recent Python versions.

The source of this problem is that `argparse` uses `regex` module to replace some substrings. Direct link: https://github.com/python/cpython/blame/8ce20bbdd6d2b1277a5e74154fcdcef2cb0fee49/Lib/argparse.py#L487

Quick debug showed that without this line these tests fail:

```
======================================================================
FAIL: test_help_when_required (test.test_argparse.TestMutuallyExclusiveFirstSuppressed)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_argparse.py", line 2649, in test_help_when_required
    self.assertEqual(format_help(), textwrap.dedent(help))
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 'usage: PROG [-h] (-y)\n\noptions:\n  -h, --help  show this[42 chars]lp\n' != 'usage: PROG [-h] -y\n\noptions:\n  -h, --help  show this h[40 chars]lp\n'
- usage: PROG [-h] (-y)
?                  -  -
+ usage: PROG [-h] -y
  
  options:
    -h, --help  show this help message and exit
    -y          y help


======================================================================
FAIL: test_usage_when_required (test.test_argparse.TestMutuallyExclusiveFirstSuppressed)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_argparse.py", line 2639, in test_usage_when_required
    self.assertEqual(format_usage(), textwrap.dedent(expected_usage))
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 'usage: PROG [-h] (-y)\n' != 'usage: PROG [-h] -y\n'
- usage: PROG [-h] (-y)
?                  -  -
+ usage: PROG [-h] -y


======================================================================
FAIL: test_help_when_required (test.test_argparse.TestMutuallyExclusiveFirstSuppressedParent)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_argparse.py", line 2649, in test_help_when_required
    self.assertEqual(format_help(), textwrap.dedent(help))
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 'usage: PROG [-h] (-y)\n\noptions:\n  -h, --help  show this[42 chars]lp\n' != 'usage: PROG [-h] -y\n\noptions:\n  -h, --help  show this h[40 chars]lp\n'
- usage: PROG [-h] (-y)
?                  -  -
+ usage: PROG [-h] -y
  
  options:
    -h, --help  show this help message and exit
    -y          y help


======================================================================
FAIL: test_usage_when_required (test.test_argparse.TestMutuallyExclusiveFirstSuppressedParent)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_argparse.py", line 2639, in test_usage_when_required
    self.assertEqual(format_usage(), textwrap.dedent(expected_usage))
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 'usage: PROG [-h] (-y)\n' != 'usage: PROG [-h] -y\n'
- usage: PROG [-h] (-y)
?                  -  -
+ usage: PROG [-h] -y


----------------------------------------------------------------------
Ran 1672 tests in 23.258s

FAILED (failures=4)
test test_argparse failed
test_argparse failed (4 failures)

== Tests result: FAILURE ==

1 test failed:
    test_argparse

Total duration: 25.6 sec
Tests result: FAILURE
```

Maybe instead we can show users something like:

```
usage: ex.py [-h] (-p '/var/www/html' | -r 'http)s(://Host:Port') [--last-args LAST_ARGS]
```

?

The usage formatting is fragile, with many associated bug reports.  Until someone does a major rewrite, it is best to avoid special characters, especially `()` and `[]` in the `dest` or `metavar`.

Usage uses () to encolde mutually_exclusive_groups and [] to mark non-required arguments.  Don't confuse your users (or argparse) with other uses of these characters.