[Homebrew] Add the ability to Homebrew "rules"

Sometimes when homebrewing content there are common elements between races, sub-classes etc. that don't really make sense belonging to just one, but need to be duplicated to make them available to both.

For example, with my Brute (Large) Races there are common elements between them owing to their being Large creatures, specifically the Large Creature and Large Weapons sections.

To avoid this kind of duplication, I'd like to propose the ability to homebrew "rules", these would be an extremely simple Homebrew type with a full description and an optional summary and snippet. The idea is that these can then be combined with special race and sub-class traits that simply embed the rule using either the full description, or just summary with an option to view the full description, if a summary was provided. If the rule is imported into a feature/trait that displays on the character sheet, then a provided snippet will be used.

So for my Brute (Large) races I might create a Large Creature rule, and add a racial trait with the Rule box set to Large Creature. Instead of having to fill in any further details, D&D Beyond would then simply import my Large Creature "rule" to the race, placing its description onto my race(s), and using its snippet for characters that use those race(s).

This feature would be complemented well by the proposal to allow tooltips to reference homebrew content, by allowing us to define items to reference via [rule] tags.