[openusd_internal] Fix more symbol leaks

[rpoyner-tri]

• pegtl_namespace.patch

This patch allows the drake_vendor namespace modifications to be reflected in TAO_PEGTL_NAMESPACE, which in turn allows the resulting symbols to be matched by allow lists in exported_symbols_test.

• work_thread_limits_namespace.patch

This patch puts some macro-generated globals inside the library namespace.

• Also, alpha-sort the patch file names.

---

This change is 

[jwnimmer-tri]

Sorry, my message crossed in the wind. See https://github.com/RobotLocomotion/drake/pull/21549#issuecomment-2155157624.

This should be pushed into #21405, so that we have CI coverage if it's impact / importance.

I also see now the #21405 has already blown well past the 1500 line limit, and has been in flight for weeks, so it's probably time to carve out and finish enough of it to capture ground and hold it -- e.g. just parsing spheres, ignoring inertias, or whatever. We should bootstrap its testing infra (and symbol leak plugging) before starting to pile on all of the actual details of geometry parsing.

[rpoyner-tri]

Closing, in favor of direct application to the the parsing pr.