Fix Web Accessibility output not tracking background color changes

[limzykenneth]

Resolves #6610

Changes:

The text in textOutput and gridOutput previously only updates when there are changes on the canvas relating to shapes but it won't update if the background color changes while the shapes on the canvas stays the same, resulting in potentially incorrect background color being reported.

This fix adds an additional property to the web accessibility ingredients object that keep tracks of background color changes pBackground plus a check that will re-render the background color when necessary.

PR Checklist

• npm run lint passes
• Inline documentation is included / updated
• Unit tests are included / updated