Improve the UX for inviting users to rooms

The RoomInviteSheet can use some UX improvement for searching up users and validating user input. Currently the sheet is is implemented as follows:

Some disadvantages mentioned:

• There is a separate 'add' button to add a user id to the pending invite list as well as tapping a search suggestion. Would it be simplier to remove the add button and only use the search suggestions for adding users to the list?

• Having the 'add' button requires us to validate the input and report errors to the user. We need to validate that:

  • The user ID is valid & exists
  • The user ID is not in the joined members, invited members, or banned members list for the room However if we treat the text field input like on Android where it is only a search text field, no errors really need to be reported as invalid search entries will only need to be displayed as "No results found"

• Having an 'add' button removes the space of adding the 'clear text' (X) button for the text field

• Screen space is divided in half between listing search suggestions and listing the pending users to invite. On Android the full screen is available for listing suggestions. When users are selected the relevant entry is highlighted in the suggestions list.