Autocomplete results persist after hiding keyboard, on Android

[gnprice]

This is a variation on #1097. Repro:

• On Android, visit a message list that has a compose box.
• Touch the content input and enter the start of an autocomplete query, for example @a, so that autocomplete results appear.
  • Or touch the topic input and enter the first character of some existing topic, so that topic autocomplete results appear.
• Dismiss the keyboard using either (a) the "back" gesture or button or (b) the keyboard's own button for being dismissed.
• The keyboard will vanish, making room again for the full height of the message list.
• Expected: The autocomplete results will also vanish.
• Actual: The autocomplete results remain, obscuring part of the message list.

Reported by @shivanshsharma13: https://chat.zulip.org/#narrow/channel/48-mobile/topic/Dismiss.20keyboard.20and.20shift.20focus.20when.20tap.20background/near/1989970

This symptom is potentially more annoying than #1097. OTOH it's avoidable by simply deleting whatever query had pulled up autocomplete results.