[SDK] Button and icon do not have registered dependencies

[aaronreed708]

Problem/Concern

Related to #1061. I noticed in that issue that the fact that gradient1 and gradient2 doesn't have values will prevent anyone from giving the colorTheme.button a new value. Yet, button and icon do not have gradient1 and gradient2 as dependencies. This seems like an oversight. I also believe that colorTheme.primary should be a dependency for button and icon.

We probably need to determine if this worked at one time or have button and icon never had dependencies? If not, is there a reason why not? @evangk6 or @lwnoble do you know?

Proposed Solution