ui: Tooltips at the top of the screen should open downward, out of device inset

[chrisbobbe]

In beta feedback, a user reported that the "Channel feed" tooltip in the app bar of the topic-narrow message list was opening upward and getting hidden in the device inset:

On the right top side is "channel feed" button. If you are in portrait mode and long press it, description is overlaping with "notification area (signal indicator, battery stat....)". It's ok in landscape mode.

Here's how it looks on one device. The tooltip is still mostly visible here, but that won't always be the case. Some devices might cover up the tooltip with more things in that reserved space.

If opening a tooltip upward would put it in that reserved space at the top, we should open it downward instead.

[Vardhan-ysh]

I want to work on this issue. Can I be assigned to this?

[gnprice]

@Vardhan-ysh Welcome. See our guide to picking an issue to work on:
https://zulip.readthedocs.io/en/latest/contributing/contributing.html#picking-an-issue-to-work-on

I think this won't be a good issue for a contributor new to the project.