Make HEIF conversion opt-in

[swissspidy]

Maybe a general toggle such as "Convert incompatible images to web safe formats" and then this can also cover things like TIFF or JPEG 2000 or JPEG XL which don't work in (all) browsers.

Relevant core ticket: https://core.trac.wordpress.org/ticket/53645

[swissspidy]

This could also work like this:

1. Drop HEIF item into editor
2. Get presented with a modal that says the image format and is not supported by all browsers. Would you like to convert this to a web safe format?
   • Yes, always convert
   • No, upload as-is, with the downside that there won't be any thumbnails etc. (Only really works in Safari)
   • Cancel upload

[swissspidy]

Some good considerations over at https://core.trac.wordpress.org/ticket/53645#comment:12

[swissspidy]

Related: I don't think HEIC warrants an extra setting like this:

Could be much simpler with a "Convert non-web-safe images like HEIC to web-safe format" checkbox, then use the "default image format" value for that.

[swissspidy]

Aside: this is missing a "default image quality" checkbox

[swissspidy]

Closing in favor of #578