node:summary token relies on non-default field in 11.3+

Problem/Motivation

As of 📌 Stop automatic storage creation of body field Active in 11.3, the old "body" field is no longer automatically created for nodes. As a result, new sites built with 11.3+ will no longer have output in the [node:summary] token. This token is widely used by contrib modules, including Metatag for SEO purposes, and has long been perceived as the default for outputting a teaser or extract of the node's body text, leading to problems if the field doesn't exist ( 🐛 "summary" token for text+summary field is empty when using anything other than the core "body" field Active ).

This field is no longer available therefore the token will no longer output anything, therefore the token is useless.

Steps to reproduce

Build a site with 11.3+.
Output the [node:summary] token for a node.
Note that the output is always empty.

Proposed resolution

Work out a long term solution for providing a "summary" text output for a node, to inherit the purpose of the original [node:summary] token.
It might be worthwhile to make this entity-agnostic.
Update existing logic.

Remaining tasks

Work out what to do.
Do it.

User interface changes

TBD

Introduced terminology

TBD

API changes

TBD

Data model changes

TBD

Release notes snippet

TBD