We add the support for hotkey hints for the tippyjs tooltips through
the hotkey_hints handlebar helper.
The hotkey_hints helper takes space seperated string arguments and
returns a span containing all the hotkeys with the required classes
for styling.
We also add a simple node test for the hotkey_hints handlebar helper.
Part of #21753
This reverts commit f81cc16a0f (#17999).
The {{#tr}} helper now includes the functionality that we wanted from
this.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
