Update deprecated loadRevision() call for Drupal 11

Problem/Motivation

undo functionality called EntityStorageInterface::loadRevision(), which was removed from Drupal 11.0.0. Presumably undo will fail in D11.

Steps to reproduce

• Open codebase in an IDE with Intellisense. Observe strikethrough of deprecated method call (see attached screenshot from VS Code).
• Presumably, install this module in a Drupal 11 installation. Perform a replace, then attempt to undo the replace. Should receive a runtime error.

Proposed resolution

Change Node::undo() and Paragraph::undo() to use \Drupal\Core\Entity\RevisionableStorageInterface::loadRevision

Remaining tasks

User interface changes

None.

API changes

Data model changes