Add more documentation for ModuleSpec.loader_state.

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-10-04.14:51:53.047>
labels = ['3.11', '3.9', '3.10', 'docs']
title = 'Add more documentation for ModuleSpec.loader_state.'
updated_at = <Date 2021-10-23.17:03:40.736>
user = 'https://github.com/ericsnowcurrently'

bugs.python.org fields:

activity = <Date 2021-10-23.17:03:40.736>
actor = 'FFY00'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2021-10-04.14:51:53.047>
creator = 'eric.snow'
dependencies = []
files = []
hgrepos = []
issue_num = 45364
keywords = []
message_count = 1.0
messages = ['403141']
nosy_count = 6.0
nosy_names = ['barry', 'brett.cannon', 'ncoghlan', 'docs@python', 'eric.snow', 'FFY00']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue45364'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']