Changeset 49763 for trunk

Bundled Themes: Bump theme versions ahead of WordPress 5.6.

The following theme versions will be released in coordination with WordPress 5.6:

• Twenty Ten: 3.2
• Twenty Eleven: 3.6
• Twenty Twelve: 3.3
• Twenty Thirteen: 3.2
• Twenty Fourteen: 3.0
• Twenty Fifteen: 2.8
• Twenty Sixteen: 2.3
• Twenty Seventeen: 2.5
• Twenty Nineteen: 1.8
• Twenty Twenty: 1.6
• Twenty Twenty-One: 1.0

Props peterwilsoncc, hareesh-pillai, dkarfa, sabernhardt, poena, aristath, SergeyBiryukov.
Fixes #51919.