Fluid inputs: FluidForm

[tay1orjones]

Once all the fluid form components are done we'd like to have a cohesive FluidForm example to showcase all the fluid form components.

It may not be a component, but as a concept, you're going to have a "fluid form". The interoperability of the multiple components together in concert - how they behave and visually work. How focus states look, etc. Full list below:

Implementation concerns:

• Potentially adding a form header or form footer
• Remove outer margins from the modal in the example (dependent on [Feature Request]: Modal to allow full width & full height content #11933)
• Fix focus states - inset outlines, conflicting borders

#12453 (comment)

Spec