[FIX] web_editor: make fa icons work with gradient on apple devices

Step to reproduce:
- Go to Website Editor
- Add a block like Text-Image
- Change the Font Color for the title to a "Gradient"
- Add an icon in the title
-> The icon is not displayed on iphone

Note that it was probably working with commit [1] but not anymore with
commit [2].

Note also that it only seems to impact Iphone (Chrome/Safari) and MAC
(Safari only).

[1]: https://github.com/odoo/odoo/commit/187acb938f70a2130d25fa76079221339c742f1e
[2]: https://github.com/odoo/odoo/commit/372eeebb47b93890d567185879981e817cdc1326

opw-3614325

closes odoo/odoo#146420

X-original-commit: 1eda1c494a5c4accd1aadf1466bd60cca45bcaa7
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>
Signed-off-by: Romain Derie (rde) <rde@odoo.com>

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

@@ -814,6 +814,12 @@ section, .oe_img_bg, [data-oe-shape-data] {
         -webkit-background-clip: inherit;
         -webkit-text-fill-color: inherit;
     }
+
+    // On Iphone (Safari & Chrome) and Mac (only Safari), the font awesome icons
+    // are not rendered (invisible) when inside a gradient.
+    .fa {
+        display: inherit;
+    }
 }
 
 /* QWEB */