Improve Settings for Modern Image Formats

[adamsilverstein]

Feature Description

Since adding AVIF and <picture> element support, some potential improvements to the settings screen became apparent.

Potential Improvements

• As @joemcgill mentioned in Add picture element support #73 (comment) we should properly handle sites that lack both AVIF and WebP support (~2% of sites).
• <picture> element support is only useful when there is both a modern format (WebP/AVIF) and a JPEG fallback available for each sub size, eg. when the "Also output JPEG images" setting is enabled. Therefore, maybe the picture element support toggle should only be enabled when JPEGs are being generated? (and otherwise displayed in a greyed out "disabled" state)

[westonruter]

@adamsilverstein Good points. Could this be done for the next release on June 6th?

[adamsilverstein]

@adamsilverstein Good points. Could this be done for the next release on June 6th?

Sure I am happy to work on this unless someone else wants to pick it up!