IDLE: Add keyboard equivalents for mouse actions.

GitHub fields:

assignee = 'https://github.com/terryjreedy'
closed_at = None
created_at = <Date 2016-07-26.00:54:51.365>
labels = ['expert-IDLE', 'type-bug', '3.10']
title = 'IDLE: Add keyboard equivalents for mouse actions.'
updated_at = <Date 2020-06-07.22:00:04.640>
user = 'https://github.com/terryjreedy'

bugs.python.org fields:

activity = <Date 2020-06-07.22:00:04.640>
actor = 'terry.reedy'
assignee = 'terry.reedy'
closed = False
closed_date = None
closer = None
components = ['IDLE']
creation = <Date 2016-07-26.00:54:51.365>
creator = 'terry.reedy'
dependencies = ['27621']
files = []
hgrepos = []
issue_num = 27620
keywords = ['patch']
message_count = 7.0
messages = ['271311', '271312', '271331', '271345', '271480', '271483', '296570']
nosy_count = 4.0
nosy_names = ['terry.reedy', 'python-dev', 'serhiy.storchaka', 'ZackerySpytz']
pr_nums = ['19706']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue27620'
versions = ['Python 3.10']