feat(designer): added support for creating designer plugins automatically

bec_widgets/utils/plugin_templates/plugin.template

@@ -0,0 +1,54 @@
+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+from qtpy.QtDesigner import QDesignerCustomWidgetInterface
+from qtpy.QtGui import QIcon
+
+{widget_import}
+
+DOM_XML = """
+<ui language='c++'>
+    <widget class='{plugin_name_pascal}' name='{plugin_name_snake}'>
+    </widget>
+</ui>
+"""
+
+
+class {plugin_name_pascal}Plugin(QDesignerCustomWidgetInterface):  # pragma: no cover
+    def __init__(self):
+        super().__init__()
+        self._form_editor = None
+
+    def createWidget(self, parent):
+        t = {plugin_name_pascal}(parent)
+        return t
+
+    def domXml(self):
+        return DOM_XML
+
+    def group(self):
+        return ""
+
+    def icon(self):
+        return QIcon()
+
+    def includeFile(self):
+        return "{plugin_name_snake}"
+
+    def initialize(self, form_editor):
+        self._form_editor = form_editor
+
+    def isContainer(self):
+        return False
+
+    def isInitialized(self):
+        return self._form_editor is not None
+
+    def name(self):
+        return "{plugin_name_pascal}"
+
+    def toolTip(self):
+        return "{plugin_tooltip}"
+
+    def whatsThis(self):
+        return self.toolTip()

bec_widgets/utils/plugin_templates/register.template

@@ -0,0 +1,15 @@
+def main():  # pragma: no cover
+    from qtpy import PYSIDE6
+
+    if not PYSIDE6:
+        print("PYSIDE6 is not available in the environment. Cannot patch designer.")
+        return
+    from PySide6.QtDesigner import QPyDesignerCustomWidgetCollection
+
+    {plugin_import}
+
+    QPyDesignerCustomWidgetCollection.addCustomWidget({plugin_name_pascal}Plugin())
+
+
+if __name__ == "__main__":  # pragma: no cover
+    main()