[FIX] website, *: enforce correct UI text-muted color

* web_editor

- Restore the preservation of Odoo text-muted color (the rule became
  !important with BS4 and had thus to become !important in the
  preservation mixin).
- Preserve base design in the "new content" menu (which now uses
  text-muted). Indeed, in some themes, the "new content" links were not
  even visible anymore.

closes odoo/odoo#28666

addons/web_editor/static/src/scss/web_editor.variables.scss

@@ -71,7 +71,7 @@ $o-we-switch-inactive-color: $o-we-color-paper !default;
     color: $o-we-color-divider;
 
     .text-muted {
-        color: $o-we-color-text-normal;
+        color: $o-we-color-text-normal !important;
     }
 }
 

addons/website/static/src/scss/website.ui.scss

@@ -298,6 +298,7 @@ body .modal {
 }
 
 #o_new_content_menu_choices {
+    @include o-w-preserve-base;
     @include o-position-absolute($o-navbar-height, 0, 0, 0);
     position: fixed;
     display: flex;