276 ft adv drawing media whiteness

Description of feature

Can emphasize drawings in Adv. Drawing workspace.

Value consistent between Main and Adv. Drawing workspaces.

startup.blend: Passepartout value in Adv. Drawing is fully black by default to be consistent with the Sequencer's Preview.

How to test it

• Adv. Drawing
• Change value

Checklist

Please check if your MR fulfills the following requirements:

• Unit tests have been added, if possible
• Documentation has been updated
• Build was run locally and any changes were pushed
• Lint has passed locally without error
• CHANGELOG.md has been updated

FYI: @strangenoise