feat: Add labels for Toolbox and Flyout content containers (experimental)#9483

BenHenning merged 1 commit intoRaspberryPiFoundation:add-screen-reader-support-experimentalRaspberryPiFoundation/blockly:add-screen-reader-support-experimentalfrom

BenHenning:add-labels-for-toolbox-and-flyoutBenHenning/blockly:add-labels-for-toolbox-and-flyoutCopy head branch name to clipboard