Textarea support for input groups

The append and prepend classes vertically aligned items in the center
For textareas this meant the addon would aling vertically instead of stretch and have it's contents vertically aligned
these changes fix that so everything is aligned how it should be

Author: gijsbotje

scss/_input-group.scss

@@ -60,7 +60,6 @@
 .input-group-prepend,
 .input-group-append {
   display: flex;
-  align-items: center;
 
   // Ensure buttons are always above inputs for more visually pleasing borders.
   // This isn't needed for `.input-group-text` since it shares the same border-color
@@ -88,6 +87,8 @@
 // to prepend or append to an input.
 
 .input-group-text {
+  display: flex;
+  align-items: center;
   padding: $input-padding-y $input-padding-x;
   margin-bottom: 0; // Allow use of <label> elements by overriding our default margin-bottom
   font-size: $font-size-base; // Match inputs