We now make sure our toggler exists before invoking its `goto`
method. Usually a toggler exists pretty early during app
startup, but _setup_info_overlay is wrapped in i18n.ensure_i18n,
which asynchronously fetches translation data.
This commit also simplifies how we find the toggler, by just
storing it in the module where it gets created and consumed.
Fixes#9085.
For info overlays (keyboard/markdown/search help) we now let
the modal portions of the widget have focus, so that you can
page around. And then tab switching still works with the arrow
keys.
There are several ways we open help for keyboard shortcuts,
markdown help, and search operators.
- from the gear menu
- from the compose box
- from the search box
- hitting ? for keyboard help
- arrowing/clicking through the tabs
This just moves the relevant code into a module and changes a
bunch of one-line calls in various places.
