Issue #3537076 Add search input and bundle-labeled, sorted options

Issue #3537076

This update enhances the multiselect field widget in two important ways:

1. Search Input for Available Options
2. Adds bundle labels to entity reference options and sorts them alphabetically.

Test Steps:

1. Go to a form with a multiselect field.
2. In the Available options list, type into the search box above it.
3. Confirm the list filters in real time to match your search text.
4. Clear the search and see all options again.