Add support for AI submodule "ai_translate" FieldTextExtractor plugin

Linking issue in AI module, that complicates this functionality.

I assume we would need to create our own plugin for field type 'custom' similar to these: https://git.drupalcode.org/project/ai/-/tree/1.2.x/modules/ai_translate/....

Would have to loop over the subfields and check for subfield translatable setting, max-length, etc... This is all doable but I don't know alot about the AI module yet and how exactly this works so if you want to take a stab at a patch, I'd be happy to review it.

Thanks for the feedback. I'm working on a fix. Might take me a few days to push some code though...

OK I think this should be doable, but it would require the patch in ✨ Don't hardcode 'value' key for textual field translation Active to be committed first.
Not sure how fast that can happen, so this extra plugin probably won't be committed into custom_field, before that issue is resolved.
I'll try to get the MR here working in combination with that issue, and hopefully keep it as simple as possible.

Currently there is some logic that checks if a custom_field subfield / property is translatable or not.
But ideally that should check if that subfield is textual or not. Is there some mechanism in place to do that?
I guess just doing checks on CustomFieldType plugin instances? I.e. StringType & StringLongType?

Thats probably the simplest way. There's technically other subfield types like LinkType that has a title property if you wanted to account for that and more complex types (MapType, MapStringType) but the widgets for those are a bit more complex so you way want to just keep it simple for now.

Oh and the ImageType has title/alt fields. You could also loop over the property definitions (skip the computed) and account for DataDefinition class of string. The only field that differs there is the StingLongType as it has a custom class to make it work with jsonapi and such. You would still want to check for the subfield being translatable along with these checks. They won't be exposed otherwise and inherit the default language value.