[FIX] website, *: properly stack the bg layers for big boxes snippet

*: web_editor

The big boxes snippet's content was appearing below the background
layers (filters, shape, video, etc).

Part of https://github.com/odoo/odoo/pull/58192

X-original-commit: f1bd8bc7ef8b084168816bc22d821acdffe2aaf6

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

@@ -751,6 +751,7 @@ blockquote {
 }
 %o-we-background-layer {
     @include o-position-absolute(0, 0, 0, 0);
+    position: absolute !important;
     display: block;
     overflow: hidden;
     background-repeat: no-repeat;

addons/website/static/src/snippets/s_color_blocks_2/000.scss

@@ -13,6 +13,7 @@
         }
     }
     [class*="col-lg-"] {
+        @extend %o-we-background-layer-parent;
         padding: 8% 5%;
         padding-top: 8vw; // A flex item cannot have % padding top and bottom (even if it works on chrome)
         padding-bottom: 8vw; // Solution is vw units but we keep 8% as a fallback