PyQt demo app (#21625)

* build python helpers lib

* call setMainWindow from python

* put in helper lib

* linter

* move to scripts
old-commit-hash: 25e4e94691d90f1a4496a2742c63ede108593e15

scripts/pyqt_demo.py

@@ -0,0 +1,14 @@
+#!/usr/bin/env python3
+
+from PyQt5.QtWidgets import QApplication, QLabel  # pylint: disable=no-name-in-module, import-error
+from selfdrive.ui.qt.python_helpers import set_main_window
+
+
+if __name__ == "__main__":
+  app = QApplication([])
+  label = QLabel('Hello World!')
+
+  # Set full screen and rotate
+  set_main_window(label)
+
+  app.exec_()