mod_dav: Do not advertise disabled TRACE

[arturobernalg]

dav_method_options() builds its own Allow field and currently lists TRACE unconditionally for existing DAV resources.

With TraceEnable off, an OPTIONS request therefore advertises TRACE even though an actual TRACE request is rejected.

Respect TraceEnable when building the DAV Allow field.

PR 70264.

Tests cover TraceEnable off, on, and extended.

---

• This PR does not report or address a security vulnerability
  (see SECURITY.md and
  https://www.apache.org/security/#reporting-a-vulnerability).
• Code follows the httpd style guide.
• New log messages (level debug or higher) use an empty APLOGNO() tag;
  numbers are assigned by a committer at merge time (see docs/log-message-tags/README).
• If the change is user-visible, a changes-entries/*.txt file is included,
  following the template in README.CHANGES (not needed otherwise).
• Test cases based on pyhttpd are included where appropriate, in the
  test/modules/xxx directory matching the modules/xxx module source,
  or test/modules/core for core server changes. On Unix, verify these
  pass locally with e.g. make check-pytest PYTEST_DIRS=test/modules/xxx.