Use mobile-friendly font size for tag editor input field

Match other input fields in the sidebar in using a larger font size for
the tag editor input on mobile/touch inputs. This also prevents iOS
Safari from zooming into the input when focused.

src/styles/sidebar/components/tag-editor.scss

@@ -9,6 +9,10 @@
     &:focus {
       @include forms.form-input-focus;
     }
+
+    @media (pointer: coarse) {
+      font-size: var.$touch-input-font-size;
+    }
   }
 
   &__tag-list {