HUE-7148 [frontend] Set a default size for SVG icons inside buttons

desktop/core/src/desktop/static/desktop/less/hue-cross-version.less

@@ -543,4 +543,8 @@ ul.errorlist {
   z-index: 1000;
   padding-left: 20px !important;
   border-top: 1px solid @cui-gray-100;
-}
+}
+
+.btn > svg.hi {
+  font-size: 16px;
+}