Start Chat Screen: Change 'x' to back arrow & back arrow to 'x'

### Your use case

From the All chats screen: When you hit the plus button (FAB) and the Start chat screen opens, there is an X on the top left.
Nothing was created that needs to be cancelled or removed, so this X button could simply be a back button.

1. 'Start chat' > 'New room'
This is a creation screen. Your work is not saved if you press the back button. This screen is better suited for an 'x' button.

2. 'Spaces" > "New space'
This is a creation screen. Your work is not saved if you press the back button. This screen is better suited for an 'x' button.

### Have you considered any alternatives?

_No response_

### Additional context

1. The 'Start chat' screen isn't primarily a creation screen.
It presents other options and so the 'X' button can simply be a back button.

### Are you willing to provide a PR?

No

Search the Android/Kotlin UI implementations for the Start chat, New room, and New space screens, then trace the top-left navigation icons and their actions. Update the icons so Start chat uses a back arrow while the creation screens use an X, and verify each screen navigates or dismisses as described.

Written by the indexing model from the issue text.