Add clean script to TypeScript projects

[ejizba]

In model v4, the entrypoint is a glob (dist/src/functions/*.js) meaning if you delete a ts file in src, you also need to delete the js file in dist otherwise the function will still show up. This can be confusing, so probably worth adding a clean script.

A few notes:

• rimraf v5 works in Node.js v14+, but I feel like that's fine since Node 12 was EOL April 2022
• There's not as much value when adding this to the old model, but I thought it was easier to keep them consistent
• I'm pretty sure my test changes work, but obviously I wasn't able to do a full test run given the state of the tests

[nturinski]

I'm pretty sure my test changes work, but obviously I wasn't able to do a full test run given the state of the tests