MM-44122, MM-54124: Group Info/Mentions bottom sheet and invite group members to channel

[calebroseland]

Summary

• New Group Info bottom sheet for Group Mentions
• user_list UI changes—styling configuration and flex layout more streamlined
• Invite group members to channel
• Fixes bug where GM member count limit was applied to Channel -> Add Members flow
• Fixes bug where GM member count limit could be exceeded by continuing to select profiles after limit is reached

Ticket Link

• https://mattermost.atlassian.net/browse/MM-44122
• https://mattermost.atlassian.net/browse/MM-54124

Checklist

• [Pending] Added or updated unit tests (required for all new features)
• Has UI changes
• Includes text changes and localization file updates
• Have tested against the 5 core themes to ensure consistency between them.

Device Information

This PR was tested on: Pixel 6 Pro emulator, Android SDKv33. iPhone 15 Pro iOS 17 emulator
Testing pending: Tablet

Screenshots

CleanShot.2023-12-12.at.16.50.06.mp4

User List spacing options; revamped user_item flex layout

Release Note

Added Group Mentions bottom sheet and ability to invite group members to a channel.