Investigate/replace GlobalParserTLS thread local

[ormsbee]

Ensure this is async-safe:

xblocks-core/xblocks_contrib/problem/xmlparser.py

Lines 68 to 75 in 730174f

	class GlobalParserTLS(threading.local):
	"""Thread local context for custom parser instances"""
	parser_config = {
	"resolve_entities": False,
	}
	element_class = RestrictedElement

Because we're in a transitional state, this overlaps with the equivalent code that's still in openedx/openedx-platform#38698