feat: Automatically detect debug tasks

[CsCherrYY]

part of #1088, more details can be found in that issue.

fix #394, #1118, supersede #398, #1138

this PR changes:

• Automatically detect debug tasks, supersede and deprecate setting gradle.javaDebug
  • Support to debug JavaExec and Test tasks
  • for clean cache configuration, use a new configuration gradle.javaDebug.cleanOutput instead
  • in proto file, add a new field debuggable in GradleTask, which contains the task type from custom Gradle model.
• Rewrite document about debugging feature

[CsCherrYY]

verify steps:

1. Download https://docs.gradle.org/current/samples/zips/sample_building_java_applications-groovy-dsl.zip
2. In ./app/build.gradle, add the following snippet

task runApp(type: JavaExec) {
  classpath = sourceSets.main.runtimeClasspath
  mainClass = 'demo.App'
}

3. In ./app/src/main/java/demo/App.java, add a breakpoint at line 12 (System.out.println(new App().getGreeting());)
4. open Gradle projects view, find runApp task in app project, Tasks -> other -> runApp
5. can see the debug button in the task, and click this button to successfully debug the task.

[Eskibear]

verified.