Detecting if a virtual keyboard will open if an element gets focus

In our chat application, we often move focus back to the message field after an action such as deleting a message has been performed. Unfortunately, this opens up the virtual keyboard in many cases, so we disable this behavior if we think we're on a mobile device. We currently check this using screen size, but that's not a great heuristic.

It would be great if there were a way to check if moving focus to an input or contentEditable element would cause an on-screen keyboard to open. We might be able to solve this with the inputPanelPolicy proposed in #225, but that would mean blocking the keyboard by default, and then re-enabling it in the cases when we want it to appear, and I'd prefer to do it the other way around.

Start by reading the issue and the referenced inputPanelPolicy proposal in #225. Clarify whether the desired outcome is a new way to detect keyboard opening or a different focus policy, then document an agreed specification direction; no file or test is named in the issue.