IDLE help viewer: let users control font size

[terryjreedy]

BPO	33397
Nosy	@terryjreedy, @csabella
PRs	gh-77578: IDLE Help - let users control font size #6665

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/terryjreedy'
closed_at = None
created_at = <Date 2018-05-01.05:46:36.738>
labels = ['3.8', 'expert-IDLE', 'type-feature', '3.7']
title = 'IDLE help viewer: let users control font size'
updated_at = <Date 2019-01-24.05:53:29.409>
user = 'https://github.com/terryjreedy'

bugs.python.org fields:

activity = <Date 2019-01-24.05:53:29.409>
actor = 'terry.reedy'
assignee = 'terry.reedy'
closed = False
closed_date = None
closer = None
components = ['IDLE']
creation = <Date 2018-05-01.05:46:36.738>
creator = 'terry.reedy'
dependencies = []
files = []
hgrepos = []
issue_num = 33397
keywords = ['patch']
message_count = 3.0
messages = ['315985', '315987', '334282']
nosy_count = 2.0
nosy_names = ['terry.reedy', 'cheryl.sabella']
pr_nums = ['6665']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue33397'
versions = ['Python 3.7', 'Python 3.8']

[terryjreedy]

Dependency of bpo-33396.

1. Base the initial font sizes on the on the configured editor font size. Note that editor font size defaults to 10 while the current base size is 12. I did not find any explicit discussion of this in the original issue, bpo-16893, or the first followup, bpo-25198. Perhaps Mark Roseman just liked the result, or perhaps it made the relative sizing easier.

2. Change font size with Control-Mousewheel. Manually tested code for doing this on Windows, Linux, and MacOS is in turtledemo.__main__. The three systems are wildly different. What we do here should allow easily doing same for other text windows.

[terryjreedy]

The configdialog font tab sample could also use font resizing. bpo-24776.