chore: run build before and during interactive mocha

[maribethb]

The basics

• I validated my changes

The details

Resolves

Fixes annoyance where if you modify blockly while trying to debug tests, you

1. run npm run test:mocha:interative to run the tests
2. make a change in blockly itself
3. kill the mocha server (or switch to a new terminal tab)
4. rebuild blockly
5. restart mocha server

I always forget that I have to rebuild blockly so I end up thinking my tests pass when they don't or vice versa

Proposed Changes

• Runs npm run build before launching tests, and uses concurrently and tsc watch to also rebuild on changes to core, just like we do for the playground.
• Now you just need to wait for blockly to rebuild and then refresh the mocha page

Reason for Changes

i was annoyed while writing tests

Test Coverage

no

Documentation

no

Additional Information