[FIX] web: keep compatibility for btn-fill

The class btn-fill has been move from the common bootstrap review and
only set in frontend. So we add the class in the backend to keep the
existing HTML fields containing btn-fill- class correctly working.

As there were small differences btween btn and btn-fill, we only use the
same design.

Since the classe btn-fill has been moved to only

closes odoo/odoo#125966

X-original-commit: 8ffc79624eef80d3dfdb9ad38c6faea1187a3b70
Signed-off-by: Pierre Masereel (pim) <pim@odoo.com>

addons/web/static/src/scss/bootstrap_review_backend.scss

@@ -42,6 +42,22 @@
     }
 }
 
+@each $-name, $-value in $o-btns-bs-override {
+    .btn-fill-#{$-name} {
+        @include button-variant(
+            o-safe-get($-value, background),
+            o-safe-get($-value, border),
+            o-safe-get($-value, color),
+            o-safe-get($-value, hover-background),
+            o-safe-get($-value, hover-border),
+            o-safe-get($-value, hover-color),
+            o-safe-get($-value, active-background),
+            o-safe-get($-value, active-border),
+            o-safe-get($-value, active-color),
+        );
+    }
+}
+
 // 2. Render '$theme-colors' buttons excluding the ones already generated
 //    using the custom maps.
 @each $-name, $-color in $theme-colors {