`spotlessPredeclare` accessor is not available in kotlin scripts

[bric3]

In Gradle kotlin scripts, spotlessPredeclare is not available as an assessor. In order to use this , one has to access it via the extensions API, e.g. using kotlin's with.

with(extensions["spotlessPredeclare"] as SpotlessExtension) { ... }

Looking at the codebase, I noticed the spotlessPredeclare is not created when the plugin is applied.

spotless/plugin-gradle/src/main/java/com/diffplug/gradle/spotless/SpotlessPlugin.java

Lines 51 to 52 in db6a60e

	// setup the extension
	project.getExtensions().create(SpotlessExtension.class, SpotlessExtension.EXTENSION, SpotlessExtensionImpl.class, project);

Maybe it's on purpose and I wonder why, but maybe it's not and maybe this can be added relatively easily.

[nedtwigg]

spotlessPredeclare has two modes:

spotless/plugin-gradle/src/main/java/com/diffplug/gradle/spotless/SpotlessExtension.java

Lines 327 to 343 in acc621e

	public void predeclareDepsFromBuildscript() {
	if (project.getRootProject() != project) {
	throw new GradleException("predeclareDepsFromBuildscript can only be called from the root project");
	}
	predeclare(GradleProvisioner.Policy.ROOT_BUILDSCRIPT);
	}
	public void predeclareDeps() {
	if (project.getRootProject() != project) {
	throw new GradleException("predeclareDeps can only be called from the root project");
	}
	predeclare(GradleProvisioner.Policy.ROOT_PROJECT);
	}
	protected void predeclare(GradleProvisioner.Policy policy) {
	project.getExtensions().create(SpotlessExtensionPredeclare.class, EXTENSION_PREDECLARE, SpotlessExtensionPredeclare.class, project, policy);
	}

Happy to take a PR which makes this more Kotlin-friendly.