feat: Add the IFlyoutInflater interface.

[gonfunko]

The basics

• I validated my changes

The details

Resolves

Fixes #8540

Proposed Changes

This PR adds a new IFlyoutInflater interface that will be used to create and dispose of arbitrary elements that may live on a flyout's workspace. Future PRs will add concrete implementations and refactor the flyout to use them.

Reason for Changes

This will allow for developers to add additional, arbitrary types of elements to flyouts.

[gonfunko]

Note that the gapForElement method is an addition relative to Beka's design doc. This is needed because certain elements (in particular blocks) can specify a gap in their definition, which follows the element in question. The flyout, when parsing its contents, will first get the element, then request its desired gap.