We should handle TraitsUI helpers better in GUITestAssistant

[corranwebster]

This is awkward - should perhaps just duplicate code rather than trying to import it?
See

pyface/pyface/ui/qt/util/gui_test_assistant.py

Lines 42 to 56 in 32ac8b0

	try:
	import traitsui.api # noqa: F401
	except ImportError:
	self.traitsui_raise_patch = None
	else:
	try:
	import traitsui.qt # noqa: F401
	self.traitsui_raise_patch = mock.patch(
	"traitsui.qt.ui_base._StickyDialog.raise_"
	)
	except ModuleNotFoundError:
	self.traitsui_raise_patch = mock.patch(
	"traitsui.qt4.ui_base._StickyDialog.raise_"
	)
	self.traitsui_raise_patch.start()