Support applying plugin to multiple modules

[jbarr21]

Depending on the project structure, it may be necessary to apply the plugin to multiple modules to create the required theme inheritance structure.

If we have a foundational layer (with Light & Dark) provided by module A and an intermediate layer (w/ Light & Dark) provided by module B, and then an App Layer that inherits from the intermediate layer

Currently, all ThemeStencilProviders found on the classpath will be generated into every module the plugin is applied to.