Add in a Gradle Property to enable the full execution of the the plugin, without interfering with typical Gradle Builds.

[handstandsam]

When developing invert with org.gradle.configureondemand=true, the :invert task would run on all subprojects as one would expect. In order to do this, all projects are marked as dependencies requiring a full configuration of all the projects.

In order to avoid this in standard development, we should add a flag to only do this when a report needs to be generated.

./gradlew :invert -Pinvert.enabled=true or something like this.

[handstandsam]

In a recent conversation, it sounds like this can be accomplished without subprojects if the correct inputs/outputs are specified, and Gradle will wire it up.

Here is where the code is in invert now:

invert/invert-gradle-plugin/src/main/kotlin/com/squareup/invert/InvertGradlePlugin.kt

Lines 39 to 64 in 4eb9661

	rootProject.afterEvaluate { rootProject ->
	val subprojectsToRegisterOn = rootProject.subprojects
	.filter { shouldRegisterOnSubproject(it, extension) }
	val rootInvertTask = rootProject.tasks.register(
	InvertTask.TASK_NAME,
	InvertTask::class.java
	) { reportTask ->
	reportTask.setParams(
	project = rootProject,
	subprojectInvertReportDirs = subprojectsToRegisterOn.map {
	File(
	it.layout.buildDirectory.get().asFile,
	InvertFileUtils.REPORTS_SLASH_INVERT_PATH
	).absolutePath
	}
	)
	reportTask.dependsOn(metadataTask)
	}
	subprojectsToRegisterOn.forEach { subproject ->
	// Without evaluationDependsOn, subproject won't be configured to access the dependency graph.
	rootProject.evaluationDependsOn(subproject.path)
	registerOnSubproject(subproject, rootInvertTask, invertCleanTask, extension)
	}
	}

This is bad because:

1. It uses afterEvaluate
2. It uses .subprojects
3. All of this makes it "work", but requires unnecessary configurationo.