Add support for schema.org microdata

[mainrs]

A lot of websites use microdata to add semantic meaning to their content. https://schema.org/docs/gs.html

A lot of recipe websites have this. Just to give an example: https://www.japanesecooking101.com/crab-gratin-recipe/.

[jg-l]

This is interesting, maybe in the next release after null-safety migration this weekend.