faster -PspotlessIdeHook with configure-on-demand

[nedtwigg]

Right now, the IDE hook works like this

spotlessApply -PspotlessIdeHook=${ABSOLUTE_PATH_TO_FILE}

But for large multiproject projects we could make it significantly faster with (note the leading colon)

:spotlessApply -PspotlessIdeHook=${ABSOLUTE_PATH_TO_FILE} --configure-on-demand

but only if we modified this code

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

Lines 54 to 56 in 48723eb

	@Override
	protected void createFormatTasks(String name, FormatExtension formatExtension) {
	boolean isIdeHook = project.hasProperty(IdeHook.PROPERTY);

by adding something like:

if (project == rootProject) {
 String ideHookPath = (String) project.property(IdeHook.PROPERTY);
 project.gradle.settingsEvaluated { settings -> 
 // the code below works only for root with children, needs to also handle children with children
 ProjectDescriptor owningProject = null;
 ProjectDescriptor rootDescriptor = settings.rootProject
 for (ProjectDescriptor child : rootDescriptor.children) {
 if (ideHookPath.startsWith(child.projectDir.absolutePath)) {
 owningProject = child;
 } 
 }
 if (owningProject != null) {
 project.evaluationDependsOn(owningProject.path)
 }
 }
}

In this way we can avoid evaluating all the spotlessApply tasks and instead only evaluate the root project and, if necessary, the project which contains the file in question.