Fixes wordpress-mobile/gutenberg-mobile#2106

When uploading media from the block editor without internet connection, the placeholder will hang instead of showing the retry message. This affects any block that handles media upload, Image, Video, Media & Text, and Cover.

This PR adds an internet connection check in the thumbnailReady state to avoid showing the progress bar when it is not uploading anything and display the retry message instead.

For a bit more insight, when uploading media from the media library outside the editor it won't let the user upload anything without an internet connection. In this case, we do want to start the upload process but let the user know if it failed by having no connection.

To test

• Open the app.
• Open the editor.
• Add one of these blocks: Image, Video, Media & Text or Cover.
• Turn on Airplane mode or disable any internet connection from the device.
• Tap on the block and upload a file from the device.
• Expect the block to display a retry message.
• Turn on the internet connection.
• Tap on the block and retry the upload.
• Expect the media to be uploaded successfully.

Before	After

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.