Support a deferred or passive autocompletion option

[travis-g]

Description

With command parameters that support autocomplete, if no options are returned by a bot when the autocomplete? parameter is true a large "No options match your search" dialog remains in place and cannot be cleared/dismissed, blocking the view of chat behind the dialog:

• If there's a single autocomplete option sent, the dialog shrinks down to fit just the one option.
• There is not a way to conditionally enable or disable the autocomplete option for a parameter if there are no suggestions.

Proposal

Support a "deferred" or "passive" autocomplete suggestion method where partial autocomplete interactions are sent to a bot, and if the APPLICATION_COMMAND_AUTOCOMPLETE_RESULT response contains an empty set of options there is no indicator to the user that there could have been suggestions. A "deferrable" type would align with the deferrable message component button presses, where a client ACKs a press but may respond later.

For deferrable autocompletion options the UI might expand upward as necessary from the text entry bar rather than assume a larger dialog height is needed (ex. assuming 4 options by default on mobile) and then contract as necessary. This would also prevent a large portion of the screen from being blocked by a dialog while bots resolve the suggestions.

From a UX perspective and based on implications of the "No options match your search" response text, allowing commands for bots to silently return no results facilitates a response of "there are no suggestions based on your input" rather than "you have 'searched' for options but there are no matches".