Use Gradle lazy properties for `WireExtension` API

[EdricChan03]

Gradle has been transitioning their APIs to use Property/Providers for lazy configuration (there's also now a note that JavaBeans-style configuration is discouraged) - this way, DSLs in the WireExtension interface can be set and only realised lazily when they're actually needed.

For example, a MutableList should be using the ListProperty API instead