[FIX] web_editor: force to hide the highlight options overlay on scroll

After introducing the text highlights feature in [1], the text overlay
opacity was reduced for more highlight visibility on small text, leading
to a visible text overlay even on scroll.

The goal of this commit is to fix this behaviour by forcing the opacity
to 0 when the overlay should be hidden.

[1]: https://github.com/odoo/odoo/commit/f64c9f27f1a9106bc009ad2f696845f2c5c58066

task-3285817

Part-of: odoo/odoo#142968

addons/web_editor/static/src/scss/wysiwyg_snippets.scss

@@ -2260,7 +2260,7 @@ we-select.o_we_border_preview_aligned_select {
         transition: opacity 400ms linear 0s;
 
         &.o_overlay_hidden {
-            opacity: 0;
+            opacity: 0 !important;
             transition: none;
         }
         &.oe_active {