New setting entry to let user choose project type

[akaroml]

We have projects that have multiple project info inside. Like this one:
https://github.com/spring-guides/gs-spring-boot

Both Gradle and Maven project info exists. In this case, Gradle wins by default.

The project configurations come from the source repo, but when users actually work on it, it's better to have an option to let users choose their preferred project type.

The new setting could look like:
preferredProjectType: "Gradle" // or "Maven"

And the setting could be global or per project.

[fbricon]

You can use java.import.gradle.enabled:false or java.import.maven.enabled:false, for similar results

[Eskibear]

@fbricon I tried the both settings, they work in most cases. For some reason I have such a repository, in the Utils folder, there are Maven based utils, and the main project is Gradle based. I want to import all Maven and Gradle projects, but only Gradle projects are recognized.

[Eskibear]

I think the root cause is Here, When gradle importer applies, it stops checking for other importers. So whenever there is a build.gradle file in the workspace, there would be no maven projects recognized I think.

	private IProjectImporter getImporter(File rootFolder, IProgressMonitor monitor) throws OperationCanceledException, CoreException {
		Collection<IProjectImporter> importers = importers();
		SubMonitor subMonitor = SubMonitor.convert(monitor, importers.size());
		for (IProjectImporter importer : importers) {
			importer.initialize(rootFolder);
			if (importer.applies(subMonitor.split(1))) {
				return importer;
			}
		}
		return null;
	}