Pull in dev-tools and make sure it works with core and themes plugins #7763

This is part of the monorepo project.

This is a separate issue because I anticipate some difficulty with dev-tools, since it's used by both core Blockly (for development) and by plugins. In the best case, this will be straightforward and no different from any other plugin.

• Copy dev-tools plugin from blockly-samples into blockly
• Update versions to respect locked versioning, and update dependencies to use workspace-style notation
  • @maribethb to add more detail here
• Test that npm install, npm build, and npm test work
  • From the root of the monorepo
  • From inside each plugin's directory (this plugin and theme plugins)