[FIX] web, web_editor: fix text muted within a dropdown menu

Steps to reproduce the bug:

- Install the "Blogs" app and go to the "/blog" page.
- Click on "Edit" to enter edit mode.
- Go to the "Theme" tab.
- Select the 4th color from the theme colors and choose "black".
- Save the page to exit edit mode.
- Perform a search in the search bar input that yields no results, for
example: "zzz".
- Bug: The message "No results found. Please try another search." is not
visible because it is displayed in white on the white background of the
dropdown.

A previous commit [1] had already addressed the issue for the "Search"
snippet that can be dropped into a page, but this fix wasn't sufficient
to solve the problem everywhere. Indeed, the text-muted in a dropdown
should be adjusted in all cases and not just for snippets; it's a
Bootstrap issue. The text-muted color should be adapted to the
background color of the dropdown.

[1]: https://github.com/odoo/odoo/commit/f9bf40cb53cf487c8736c1f565c2f0d3834acd5e

task-3662985

closes odoo/odoo#158203

X-original-commit: 46fcb3712f0ba68144b03ed23f52157d4dfc789a
Signed-off-by: Benjamin Vray (bvr) <bvr@odoo.com>
Signed-off-by: Outagant Mehdi (mou) <mou@odoo.com>

addons/web/static/src/scss/bootstrap_review_frontend.scss

@@ -229,3 +229,10 @@ $-color-for-gray-200-bg: adjust-color-to-background($body-color, $gray-200);
         @include border-radius($input-border-radius, 0);
     }
 }
+
+// Dropdown
+.dropdown .dropdown-menu {
+    .text-muted {
+        color: adjust-color-to-background($text-muted, $dropdown-bg, mute-color($color-contrast-light), mute-color($color-contrast-dark)) !important;
+    }
+}

addons/web_editor/static/src/scss/web_editor.common.scss

@@ -595,10 +595,6 @@ blockquote {
             }
         }
         .dropdown-menu .dropdown-item-text .text-muted {
-            // Search autocomplete messages are shown as text-muted entries.
-            // These need to be reset in case a dark palette is applied.
-            color: $text-muted !important;
-
             a {
                 // Search autocomplete's fuzzy matched term is shown as a link
                 // within an information message.