We currently support += in both Groovy and Kotlin DSLs (and << in Groovy) for eager JavaBean properties with a collection and map type, as well as for mutable FileCollection JavaBean properties.

When migrating these to ListProperty, SetProperty and MapProperty as well as ConfigurableFileCollection, it would be nice to keep the operators working in a consistent way.

It should be a goal to have the operators (where available) to work consistently across the two DSLs.

It is not a goal to make the same operators work with local variables, only with (task, transform etc.) properties.

See assignment overloads comparison between eager and lazy types: https://docs.google.com/spreadsheets/d/1F9wEuh0-pUC9eALVuR13oWfmfsFezFgG7v0oRJBG3mA/.

cc: @gradle/bt-execution