Fix Popper preventOverflow boundary config (#32845)

Currently, the boundary config is being assigned to the wrong var (`rootBoundary`) in the popper config.  It should be assigned to the `boundary` var in popper's config.

Ref: https://popper.js.org/docs/v2/utils/detect-overflow/#boundary

js/src/dropdown.js

@@ -318,7 +318,7 @@ class Dropdown extends BaseComponent {
         name: 'preventOverflow',
         options: {
           altBoundary: this._config.flip,
-          rootBoundary: this._config.boundary
+          boundary: this._config.boundary
         }
       },
       {

js/src/tooltip.js

@@ -509,7 +509,7 @@ class Tooltip extends BaseComponent {
         {
           name: 'preventOverflow',
           options: {
-            rootBoundary: this.config.boundary
+            boundary: this.config.boundary
           }
         },
         {