Refactor field widget code to reduce duplication and make theme abstract

Problem/Motivation

Both "widgets" duplicate a LOT of code. Making it seemingly impossible to effectively work on it without fear of major regressions.

Proposed resolution

Make InlineParagraphsWidget a subclass of ParagraphsWidget and simply reuse existing methods that are the same between the two.

Also, create an additional helper class, like ParagraphsWidgetItem or something to wrap a lot of the boilerplate code so it doesn't have to be determined again in the various methods called (plus it will give constraints).

Remaining tasks

• Create a patch

User interface changes

None

API changes

Technically making InlineParagraphsWidget a subclass of ParagraphsWidget is a "change", however no actual code/logic would change.

Data model changes

None