Activity bar uses the built-in VS Code product icon "$(checklist)"
from the Codicons set (https://github.com/microsoft/vscode-codicons).

media/activitybar.svg is the same "checklist" glyph, vendored for reference /
fallback, from:
  https://github.com/microsoft/vscode-codicons/blob/main/src/icons/checklist.svg

Codicons license: CC BY 4.0
  https://github.com/microsoft/vscode-codicons/blob/main/LICENSE
