`CosmicBuffer::get_text()` may return `Placeholder` value

[bytemunch]

May need to reflect the actual text value in another place to guarantee correct values returned.

Alternatively teach users to put any system using get_text() after a CosmicSet system set that encompasses all plugin systems?

[bytemunch]

Further investigation shows that my issue may be returning the underlying buffer's text instead of an active editor, which makes sense. Maybe a system ordering thing with focus stuff, maybe need an explicit apply_deferred after dropping focus?

[bytemunch]

I got tracy out and finally realised that this may be caused by focus systems running in PostUpdate whereas most user functions are run in Update, meaning that editor updates to a buffer are not applied by the time a user system tries to read them. Trying moving focus systems to Update now, if that works I'll look into moving other plugin systems out of different schedules (though I'm sure anything render-related needs to go in PostUpdate after bevy's TransformPropagate)