CI: Refactor/Reorder *.star files (#52384)

* Refactor test pipelines

* Move pr, main and release starlark files under scripts/drone/event

* Move cron.star to scripts/drone/events

* Further unused code removal

* Introducing build.star

* Extract verify_drone.star

* Extract windows.star

* Extract publish.star

* Remove unused code

* Fix formatting in main.star

scripts/drone/pipelines/verify_drone.star

@@ -0,0 +1,21 @@
+load(
+    'scripts/drone/steps/lib.star',
+    'identify_runner_step',
+    'download_grabpl_step',
+    'lint_drone_step',
+)
+
+load(
+    'scripts/drone/utils/utils.star',
+    'pipeline',
+)
+
+def verify_drone(trigger, ver_mode):
+    steps = [
+        identify_runner_step(),
+        download_grabpl_step(),
+        lint_drone_step(),
+    ]
+    return pipeline(
+        name='{}-verify-drone'.format(ver_mode), edition="oss", trigger=trigger, services=[], steps=steps,
+    )