Kibana version: Verified in 7.11.1, 7.12.0, 7.13.0-SNAPSHOT, and master

Describe the bug: Lens only shows keyword fields, not text fields

Steps to reproduce:

1. Create a test document in Dev Tools:

   POST test/_doc
   {
     "link": "https://www.example.com"
   }
   

2. Create an Index Pattern for this document:
   
3. Create a Lens Visualization:
   

Expected behavior: Lens should show both link and link.keyword in the available fields