User is notified that Gradle version is deprecated for use with plugin portal

+review
Merge branch 'plugin-portal-deprecation-messages' into release
Display deprecation messages exactly as they are returned from plugin portal

+review REVIEW-5080
make ObjectFileLanguageOutputType not internal; mark stuff as incubating

+review REVIEW-5076
add some unit test coverage for ComponentModelBasePluginTest

+review REVIEW-5076
Robustness in cancellation handling.

Catch exception(s) and rethrow them later to call all handlers.
REVIEW-5073 Log info about missing cancellation support.

Use logger in a decorator for ConsumerConnection to notify user that the
build cannot be cancelled if older toolingApi provider is used.
REVIEW-5073 Remove notice about non-working cancel from build output.
REVIEW-5090 Really reduce load in ConcurrentTestUtil.poll()
Temporarily disable test: ConfigureLogging rule interferes with other tests.
REVIEW-5092 Move project customizations of maxParallelForks to project build scripts.
Rename project#projectComponents to #componentSpecs; update release notes

+review REVIEW-5076
Add comment to potential open issue when declaring custom component.

+review REVIEW-5076
Made cancellation token available as a build service and inject into DefaultTaskGraphExecuter, rather than shipping it down through the build actions.
Changed some service implementations to implement Closeable or Stoppable
Changed CompositeStoppable to fail if an instance has a close() or stop() method and does not implement Closeable or Stoppable. This is just a temporary step to flush out any services I missed. The check will go away entirely in a subsequent step.
Made a few more things Closeable or Stoppable.
Removed unused class.
Made ConsumerActionExecutor a Stoppable.
Some tooling API spec updates.