Enhance: Implement FieldsBuilder Wrapper

[Log1x]

This would be a breaking change, but ideally I'd like to write a wrapper for ACF Builder instead of everyone using StoutLogic\AcfBuilder\FieldsBuilder directly.

This would allow me to implement field group caching (e.g. via CLI) and have better control over the final output to maybe do more stuff down the line (I don't know what yet).

This would also probably make #167 easier to implement.

Migration should be as easy as changing a line or two in every registered field/block/widget/option page.