Update PluginToolbarButton.yaml

[matkeg]

Changes

Added additional information for developers who need to track the PluginToolbarButton's active state in cases where the button's Enabled property is being toggled on and off.

Checks

By submitting your pull request for review, you agree to the following:

• [X] This contribution was created in whole or in part by me, and I have the right to submit it under the terms of this repository's open source licenses.
• [X] I understand and agree that this contribution and a record of it are public, maintained indefinitely, and may be redistributed under the terms of this repository's open source licenses.
• [X] To the best of my knowledge, all proposed changes are accurate.