Add mixins to handle RTL languages

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

js/src/common.scss

@@ -1,3 +1,4 @@
+@use "@/styles/_mixins" as *;
 @import "variables.scss";
 
 @import "~bulma";
@@ -39,7 +40,7 @@ $color-black: #000;
   border-radius: 5px;
   padding: 0.2rem;
   white-space: nowrap;
-  margin-right: 0.2rem;
+  @include margin-right(0.2rem);
 }
 
 .mention-suggestion {
@@ -48,7 +49,7 @@ $color-black: #000;
 
 .mention .mention {
   background: initial;
-  margin-right: 0;
+  @include margin-right(0);
 }
 
 .select select {