As a developer I want to use a standard and comfortable frontend JS library to interact with the webfield so that I am confident my field will continue to work and so I don't have to deal with implementation details.

Context:

Currently with javascriptField you have to work with postMessage barebones API. It's kind of tricky and exposes implemenation details. It would be nicer and more futureproof to have a Magnolia provided JS library to do the interactions with the feature.

Acceptance Criteria:

• Developer can use the postMessage if they want - it still works. Backwards compatibility for any existing extensions.
• New API - will continue to work in the future - even if the underlying postMessage usage changes.