Add support for Adw.AlertDialog

tests/samples/adw_alertdialog_responses.blp

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+using Gtk 4.0;
+using Adw 1;
+
+Adw.AlertDialog {
+  responses [
+    cancel: _('Cancel'),
+    discard: _('Discard') destructive,
+    save: 'Save' suggested disabled,
+  ]
+}

tests/samples/adw_alertdialog_responses.ui

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+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+DO NOT EDIT!
+This file was @generated by blueprint-compiler. Instead, edit the
+corresponding .blp file and regenerate this file with blueprint-compiler.
+-->
+<interface>
+  <requires lib="gtk" version="4.0"/>
+  <object class="AdwAlertDialog">
+    <responses>
+      <response id="cancel" translatable="true">Cancel</response>
+      <response id="discard" translatable="true" appearance="destructive">Discard</response>
+      <response id="save" enabled="false" appearance="suggested">Save</response>
+    </responses>
+  </object>
+</interface>