create chat flow implementation

[gtalha07]

Description:
This PR attempts to revise the current chat creation flow with more flexibility and bringing out adaptive UI aspect with the ease of creating default chat (as been currently) and in addition, ability to create DM, Group DM by selecting users.

• fixes from Improve chat #862 and direct follow up implementation of Implement create chat flow #853.
• This removes the need of using side sheet as interface and routing for it and instead will show modal based on platform .i.e. bottom sheet for mobile, dialog for larger screen sizes and desktop.
• Also the creation loading processes has been modified to use EasyLoading, making it much simpler to start a chat.

Next Steps: The next follow up PR's for this will be adding suggestions list and adding invitations for creating a default room.

[gtalha07]

Create Chat Dialog (Desktop/Larger Screens):

Create Chat Dialog (Space):

Start Group DM:

Start/Go DM:

Mobile Version:

[gnunicorn]

Great work, thanks @gtalha07 .

Just two things: one around the BuildContext being used in some weird way in two occasions; and the other to keep a link-able route in the mix and do the determination which widget to use in its route-controller (rather than have the caller figure that out).

[gnunicorn]

just that small thing left...