Fix duplicated publishing

[alexander-yevsyukov]

This PR is yet another one in the chain of requests handling the duplicated repositories issue for custom publications. There's much hope that this time we finally fixed it.

Unlike we suggested in the previous PR the problem was not because afterEvaluate was executed twice. The problem was that we asked to run it twice for two different custom publication handlers that (surprise!) got the same publishing destination repositories.

How it worked

The spinePublishing extension applied to the root project handles the "sorting" of publications. Those projects who are not listed among modulesWithCustomPublishing got StandardPublicationHandler, which does a lot of automated publishing work.

If a module goes its own publishing way via enrolling to the modulesWithCustomPublishing list, it gets CustomPublicationHandler.

This all works fine if a subproject does not have its own spinePublishing extension, which is the case for the modules packing IntelliJ IDEA into fat JARs. These modules get own spinePublishing extensions via intellij-platform-jar conventions plugin. Because of this, SpinePublishing extension in those subprojects also arranges the publishing with the same destinations, which it gets from the rootProject's extension.

This, in turn, creates own CustomPublicationHandler which runs its apply() on afterEvaluate.

How we fixed it

1. Handlers now are created via factories.
2. If there is a handler for a project (selected by its full path), it gets custom destination repositories, instead of creation of a new handler.
3. The state of applying the publication handler is remembered. So, calling apply() on afterEvaluate twice — because we have two levels of spinePublishing in the project hierarchy — does not do any harm. The real "meat" of the apply() function is done once.

Other notable changes

• Move io.spine.tools.gradle.task.ProtobufTaskName under the protobuf package #119 has been addressed by introducing an open base class in the proper package and making the deprecated class extend the new open base.