Match autocomplete icon to Claro autocomplete

Problem/motivation

Autocomplete fields are using an older-style icon to identify fields as such. Claro theme uses a magnifying glass icon for these fields. To maintain consistency, Linkit should follow suit.

Steps to reproduce

1. install vanilla Drupal 11
2. add an entity reference field to a content type
3. observe the field uses a magnifying glass icon to indicate it being an autocomplete field.

Conversely:

1. add Linkit module
2. create a link field that allows internal links
3. observe the field uses a gray circle to indicate it being an autocomplete field.

Proposed resolution

Follow what Claro uses for consistency.