Api/Gradle: Add a Gradle task for cleaning all

This patch adds cleanAll, a Gradle task that removes all generated
resources.

Signed-off-by: Wook Song <wook16.song@samsung.com>

nnstreamer-api/build.gradle.kts

@@ -117,6 +117,17 @@ android {
             dependsOn("genNnsSrc")
             dependsOn("genJniSrc")
         }
+
+        register("cleanAll", Delete::class) {
+            val generatedDirs = listOf("gst-android-build", "src")
+
+            for (genDir in generatedDirs) {
+                project.projectDir.toPath().resolve(genDir).apply {
+                    delete(this)
+                }
+            }
+            dependsOn("clean")
+        }
     }
 }