Related: #2358

Describe the bug
The Unsupported Block Editor requires an internet connection to function, but does not provide any indication to the user if their internet connection is offline.

To Reproduce
Steps to reproduce the behavior:

1. On the WordPress for iOS or Android apps, edit a post containing a block not currently supported by the mobile Block editor.
2. Click the (?) button on the unsupported block placeholder
3. Turn off the device's internet connection
4. Tap the "Edit block in web browser" option in the bottom sheet that appeared in Step 2
5. Notice the screen loads for a short time before staying blank, providing no indication that there is no internet connection

Expected behavior
Upon opening the Unsupported Block Editor, if there is no internet connection, the UI should communicate this is some way.

Screenshots

Smartphone (please complete the following information):

• Device: iPhone 7 or any other supported device
• OS: iOS 14 or any other OS
• Version: This feature is soon-to-be-released in WPiOS and WPAndroid version 15.3.