Pyface imports from non api modules

Ref: https://github.com/enthought/pyface/pull/866

With traits 6.2 we are explicitly stating in documentation that imports should come from api modules. Because of this I decided to run through pyface for any non api imports and this is the list I found:

From `traits.trait_base` there are imports of:
- ~[ ] `xgetattr`~ (see #1239)
- ~[ ] `xsetattr`~ (see #1239)
- [ ] `get_resource_path`
- [ ] `user_name_for`
- [ ] `traits_home`

~Additionally we import optional dependencies from `traits.testing.optional_dependencies`~ (pyface shouldn't do this)

From `traits.trait_list_object` we import `TraitsList` but this is a different `TraitList` from the one exposed in `traits.api`

~From `traits.version` we import `version`~

From `traits.util.resource` we import `get_path`

From `traitst.trait_notifiers` we import `set_ui_handler` and `ui_handler`

From `traitss.util.clean_strings` we import `python_name`

and from `traits.util.camel_case` we import `camel_case_to_words`

Some of these we may want to expose in an api module since they are being used? Others we may want to discourage their use in `pyface` since traits isn't meant to be a storage place for miscellaneous utilities. Or we may want to just leave them alone and break our own suggestion.