Also “bump” language level to allow `..<`

We are using Glide to load thumbnails for all shares. If the request fails,
Glide will re-attempt to fetch the image when the activity is resumed, e.g.
when you switch to another app and back.

This fixes the issue by cancelling the request on failure.

When inserting images & other media into the chat input, we add spaces
around it to make sure the text doesn't touch the resulting URL. But if the
user edits the text after, the text might touch the image again. This
sometimes is hard to see, especially if the thumbnail and the text are on
separate lines.

To overcome this, also insert spaces around the URL when textifying.

In buffer fragments, we are saving input for parallel fragments
(i.e. bubbles) on pause and restoring it on resume. On some systems,
particularly on API 27, it's possible that, when dragging from another app,
the target activity isn't actually resumed, hence this input change may fail
to be recorded. To prevent this, explicitly record the change after loading
the thumbnails.

This includes a long-postponed conversion of thumbnail logic to coroutines.
This facilitates waiting until the thumbnails are actually loaded and
applied to the string.