Update dialog_base implementation, assets and documentation

manifest.json

@@ -11,11 +11,34 @@
   "test_sources": [
     "tests/*.cs"
   ],
-  "depends": ["shell2d_base>=1", "interactive_base>=1", "effects_base>=1", "time_base>=1", "map_base>=1", "ui_base>=1"],
+  "depends": [
+    "shell2d_base>=1",
+    "interactive_base>=1",
+    "effects_base>=1",
+    "time_base>=1",
+    "ui_base>=1",
+    "expressions_base>=1"
+  ],
   "ui": [],
   "test_suites": [
-    {"id": "autoplay", "activate": ["--choices=", "--timeout="]},
-    {"id": "gdscript", "activate": ["--itest=gdscript"]},
-    {"id": "doc_shots", "activate": ["--itest=doc_shots"]}
+    {
+      "id": "autoplay",
+      "activate": [
+        "--choices=",
+        "--timeout="
+      ]
+    },
+    {
+      "id": "gdscript",
+      "activate": [
+        "--itest=gdscript"
+      ]
+    },
+    {
+      "id": "doc_shots",
+      "activate": [
+        "--itest=doc_shots"
+      ]
+    }
   ]
 }