Update placeholder text with key bindings to focus context panel and navigate history

[nathansobo]

Hopefully, this will help people understand how easy it is to add context to an inline transformation.

@as-cii @maxdeviant @rtfeldman could somebody update this to display the actual correct key bindings and ship it. I have them hard coded for now.

Release Notes:

• Updated placeholder text with key bindings to focus context panel and navigate history.

[rtfeldman]

I updated this to use the active keybinding for toggling the panel, which turns out to default to ⌘? rather than ⇧⌘? (because on a US Mac keyboard ? is shift-/ so cmd-shift-? would be like cmd-shift-shift-/ or something).

Our function to display keybindings currently renders it as Command-? instead of ⌘? - I could see arguments for and against changing that, although if we do change it, I imagine we'd want to change it everywhere and not just for inline assist.

It doesn't look like we have customizable keybindings for the history, so I left those hardcoded.

[rtfeldman]

@nathansobo if you're cool with how this looks, I can ship it. Otherwise I can look into the implications of changing the Mac keybindings (in general) to display with symbols instead of words.