IDLE option to strip trailing whitespace automatically on save

GitHub fields:

assignee = 'https://github.com/terryjreedy'
closed_at = None
created_at = <Date 2018-03-11.05:14:08.186>
labels = ['3.8', 'expert-IDLE', 'type-feature', '3.7', '3.9']
title = 'IDLE option to strip trailing whitespace automatically on save'
updated_at = <Date 2019-11-20.06:16:52.281>
user = 'https://github.com/rhettinger'

bugs.python.org fields:

activity = <Date 2019-11-20.06:16:52.281>
actor = 'terry.reedy'
assignee = 'terry.reedy'
closed = False
closed_date = None
closer = None
components = ['IDLE']
creation = <Date 2018-03-11.05:14:08.186>
creator = 'rhettinger'
dependencies = ['38862']
files = []
hgrepos = []
issue_num = 33046
keywords = ['patch']
message_count = 3.0
messages = ['313580', '356793', '357032']
nosy_count = 3.0
nosy_names = ['rhettinger', 'terry.reedy', 'ZackerySpytz']
pr_nums = ['17201']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue33046'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']