Tkinter/IDLE: preserve clipboard on closure

GitHub fields:

assignee = 'https://github.com/terryjreedy'
closed_at = None
created_at = <Date 2020-04-30.17:35:47.539>
labels = ['type-bug', 'expert-tkinter', '3.9', '3.10', '3.8', 'expert-IDLE']
title = 'Tkinter/IDLE: preserve clipboard on closure'
updated_at = <Date 2021-10-28.20:01:31.523>
user = 'https://github.com/E-Paine'

bugs.python.org fields:

activity = <Date 2021-10-28.20:01:31.523>
actor = 'primexx'
assignee = 'terry.reedy'
closed = False
closed_date = None
closer = None
components = ['IDLE', 'Tkinter']
creation = <Date 2020-04-30.17:35:47.539>
creator = 'epaine'
dependencies = []
files = ['49173']
hgrepos = []
issue_num = 40452
keywords = ['patch']
message_count = 45.0
messages = ['367765', '369002', '369135', '369156', '369165', '369199', '369287', '369304', '369322', '369334', '369338', '369383', '369387', '369389', '369391', '369392', '369395', '369406', '369440', '369444', '369453', '369456', '369601', '376354', '380199', '382635', '393742', '393743', '393750', '393753', '393755', '393756', '393757', '393770', '393788', '393790', '393794', '393795', '393797', '393798', '393804', '393805', '393806', '393817', '393818']
nosy_count = 8.0
nosy_names = ['terry.reedy', 'taleinat', 'serhiy.storchaka', 'eryksun', 'pablogsal', 'epaine', 'Spacekiwigames', 'primexx']
pr_nums = ['19819', '26163']
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue40452'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']