[ADD] survey_dropdown_simple_choice

Display "Multiple choice: only one answer" (simple_choice) survey
questions as a dropdown list instead of radio buttons, per question.

The native radios are kept (hidden by CSS) and still carry the answer:
the dropdown only clicks them, so validation, conditional questions,
"Other" comment, auto-submit and AJAX submit are handled natively.
In review / print mode, only the selected and correct answers are
displayed. Native rendering is kept when suggested answers contain
images.

Assisted-By: Claude Opus 5.5 <noreply@anthropic.com>

survey_dropdown_simple_choice/models/survey_question.py

@@ -0,0 +1,11 @@
+from odoo import fields, models
+
+
+class SurveyQuestion(models.Model):
+    _inherit = 'survey.question'
+
+    display_dropdown = fields.Boolean(
+        string="Display as dropdown list",
+        help="Display this single choice question as a dropdown list instead "
+             "of radio buttons. Ignored if the suggested answers contain images.",
+    )