[FIX] web: scope legacy indicator to debug mode

With this commit, we only display the "legacy" indicator (red/pink
background color to indicate old widgets in new views) in debug mode.

Part-of: odoo/odoo#92475

addons/web/static/src/legacy/legacy_fields.scss

@@ -1,3 +1,3 @@
-.o_legacy_field_widget > * {
+.o_debug .o_legacy_field_widget > * {
     background-color: rgba(255, 0, 0, 0.1);
 }

addons/web/static/src/legacy/scss/views.scss

@@ -3,7 +3,7 @@
  * all renderers. For field default rules, see the fields.scss file.
  */
 
-.o_legacy_kanban_view {
+.o_debug .o_legacy_kanban_view {
     border-top: 2px solid red;
 }
 

addons/web/static/src/start.js

@@ -56,6 +56,9 @@ export async function startWebClient(Webclient) {
     if (env.services.user.userId === 1) {
         classList.add("o_is_superuser");
     }
+    if (env.debug) {
+        classList.add("o_debug");
+    }
     // delete odoo.debug; // FIXME: some legacy code rely on this
     odoo.__WOWL_DEBUG__ = { root };
     odoo.isReady = true;