Allow widgets to query the user directory

### Your use case

#### What would you like to do?

As a widget creator I want to be able to use the `Invite to this room` dialog to search for other members.

#### Why would you like to do it?

The use-case is a widget that creates meeting-rooms for a user. The user should be able to easily invite members to these meetings.

#### How would you like to achieve it?

It would be helpful if widgets could open the exact same dialog that comes up when you click the `Invite to this room` in the sidebar. It should communicate the list of selected users back to the widget when the selection is confirmed.

### Have you considered any alternatives?

_No response_

### Additional context

_No response_