Function to empty trash

[rachel-fenichel]

Is your feature request related to a problem? Please describe.
Clearing the workspace fills the trashcan.
https://groups.google.com/g/blockly/c/m7e3g0TC75Y

Describe the solution you'd like

An emptyTrash function that developers can call. No associated UI for users.

Describe alternatives you've considered

Disable event before clearing the workspace, and reenable after clearing the workspace.

• This has the advantage of leaving previous items in the trashcan, as the poster wanted.

UI for user to empty trashcan.

• Doesn't rely on the developer knowing when to empty the trash, but means adding another bit of UI, likely with low usage.