LogicException in Renderer::render() still mentions renderPlain()

Problem/Motivation

Renderer::render() can throw a LogicException that says:

Render context is empty, because render() was called outside of a renderRoot() or renderPlain() call. Use renderPlain()/renderRoot() or #lazy_builder/#pre_render instead.

But renderPlain() is deprecated since #2511308: Rename RendererInterface::renderPlain() to ::renderInIsolation().

Steps to reproduce

This exception can easily be triggered with Drush:

drush ev '$build = []; \\Drupal::service(\'renderer\')->render($build);'

Proposed resolution

The exception message should tell people to use renderInIsolation() instead.

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet