Exclude content of `extracted-include-protos` and `extracted-protos` in IntelliJ IDEA

[alexander-yevsyukov]

Currently, the directories extracted-include-protos and extracted-include-protos are marked as excluded in IDEA because they are subdirectories of build. The problem is that the content of this directories is not excluded:

This makes IDEA index these directories, and suggest files in these directories in the search results. This is what we would like to avoid.

McJava should make all the directories under extracted-include-protos and extracted-include-protos as excluded in its interaction with IDEA Gradle plugin.

We do this already for the generated/source/proto/ directories. Let's extend this practice to make it yet more convenient for the users.