Kapt: Register AP classpath as an input for "generate stubs" and "kapt" tasks

...so if the annotation processor artifact is changed, annotation processing will be relaunched.

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/Kapt3KotlinGradleSubplugin.kt

@@ -303,7 +303,10 @@ class Kapt3KotlinGradleSubplugin : KotlinGradleSubplugin<KotlinCompile> {
             registerGeneratedJavaSource(kaptTask, javaCompile)
         }
 
+        kaptTask.kaptClasspath = kaptClasspath
+
         buildAndAddOptionsTo(kaptTask.pluginOptions, aptMode = "apt")
+
         return kaptTask
     }
 
@@ -321,6 +324,7 @@ class Kapt3KotlinGradleSubplugin : KotlinGradleSubplugin<KotlinCompile> {
         kaptTask.generatedSourcesDir = sourcesOutputDir
         mapKotlinTaskProperties(project, kaptTask)
 
+        kaptTask.kaptClasspath = kaptClasspath
         buildAndAddOptionsTo(kaptTask.pluginOptions, aptMode = "stubs")
 
         return kaptTask

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/KaptGenerateStubsTask.kt

@@ -20,6 +20,7 @@ import org.gradle.api.tasks.OutputDirectory
 import org.gradle.api.tasks.SourceTask
 import org.gradle.api.tasks.incremental.IncrementalTaskInputs
 import com.intellij.openapi.util.io.FileUtil
+import org.gradle.api.tasks.InputFiles
 import org.jetbrains.kotlin.gradle.plugin.kotlinDebug
 import org.jetbrains.kotlin.gradle.tasks.FilteringSourceRootsContainer
 import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
@@ -39,6 +40,9 @@ open class KaptGenerateStubsTask : KotlinCompile() {
 
     lateinit var generatedSourcesDir: File
 
+    @get:InputFiles
+    lateinit var kaptClasspath: List<File>
+
     override fun source(vararg sources: Any?): SourceTask? {
         return super.source(sourceRootsContainer.add(sources))
     }

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/KaptTask.kt

@@ -26,6 +26,9 @@ open class KaptTask : ConventionTask() {
                 || FileUtil.isAncestor(classesDir, file, /* strict = */ false)
     }
 
+    @get:InputFiles
+    lateinit var kaptClasspath: List<File>
+
     @OutputDirectory
     internal lateinit var classesDir: File