option ref: support optional part with '[=value]' or ' value'

This supports a commonly used format when it comes to optional argument:
-fauto-profile[=path], where `path` is optional part. Plus it supports
a format when space is used: -fauto-profile path.

Extends: sphinx-doc#10840
Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>

tests/roots/test-root/objects.txt

@@ -214,7 +214,8 @@ Test repeated option directive.
 
   My secret API.
 
-Reference the first option :option:`-mapi=secret` or :option:`-mapi[=xxx]`.
+Reference the first option :option:`-mapi=secret`, :option:`-mapi[=xxx]`
+or :option:`-mapi with_space`.
 
 
 User markup

tests/test_build_html.py

@@ -1773,6 +1773,7 @@ def test_option_reference_with_value(app, status, warning):
     assert 'first option <a class="reference internal" href="#cmdoption-git-commit-mapi">' in content
     assert ('<a class="reference internal" href="#cmdoption-git-commit-mapi">'
             '<code class="xref std std-option docutils literal notranslate"><span class="pre">-mapi[=xxx]</span></code></a>') in content
+    assert '<span class="pre">-mapi</span> <span class="pre">with_space</span>' in content
 
 
 @pytest.mark.sphinx('html', testroot='theming')