Fixes #13066: Add z-index to the form control feedback icons so input groups don't render on top of them

dist/css/bootstrap-rtl.css

@@ -3218,6 +3218,7 @@ select[multiple].input-lg {
   position: absolute;
   top: 25px;
   left: 0;
+  z-index: 2;
   display: block;
   width: 34px;
   height: 34px;

dist/css/bootstrap.css

@@ -2492,6 +2492,7 @@ select[multiple].input-lg {
   position: absolute;
   top: 25px;
   right: 0;
+  z-index: 2;
   display: block;
   width: 34px;
   height: 34px;

less/forms.less

@@ -292,6 +292,7 @@ input[type="checkbox"],
   position: absolute;
   top: (@line-height-computed + 5); // Height of the `label` and its margin
   right: 0;
+  z-index: 2; // Ensure icon is above input groups
   display: block;
   width: @input-height-base;
   height: @input-height-base;