Closes#1818
- Refactors image renderers, and changes the condition for which the
loading indicator is displayed from "`<data>.blobUrl` exists and has a
truthey value" to "`<data>` is not nullish"
- Adds an additional class config to the shared QA loading indicator,
and uses it in the image slider view to add a background and aspect
ratio to the loading indicator's container so that it takes up the space
it should and has an opaque background
| Before | After |
| --- | --- |
| <img width="813" alt="Screenshot 2024-05-22 at 5 17 14 PM"
src="https://github.com/webrecorder/browsertrix/assets/5727389/fb8a3a83-a0c8-46c1-b59b-a59adff2a175">
| <img width="813" alt="Screenshot 2024-05-22 at 5 17 31 PM"
src="https://github.com/webrecorder/browsertrix/assets/5727389/6fe5d04a-ffa9-4fc3-bc3b-bdb9b7b30948">
|
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