fix(build): Have prepare task signal async completion

[cpcallen]

The basics

• I branched from develop
• My pull request is against develop
• My code follows the style guide
• I ran npm run format and npm run lint

The details

Resolves

"Did you forget to signal async completion?" error from gulp when running the prepare task (as invoked by npm run prepare or npm install).

Proposed Changes

Add a done parameter and pass the provided callback to buildJavaScriptAndDeps. This also allows a simplification of the the don't-run case by simply calling done() and then returning.

Behaviour Before Change

When not run by a GitHub action, npm run prepare and npm install generate the aforementioned error.

Behaviour After Change

prepare script successfully signals async completion, avoiding error.

Reason for Changes

PR #6244 made a change to have the npm run prepare script (automatically invoked by npm install after package installation) not bother running the buildJavaScriptAndDeps gulp task when run from a GitHub action (since our build action will do npm test straight afterwards, which runs this task).

Unfortunately, due my misunderstanding of how gulp tasks work the "fix" was not correct, and somehow I overlooked the error while testing locally (and of course it was not generated in CI because the other branch of the conditional was taken).

Test Coverage

• Tested locally to verify that buildJavaScriptAndDeps is run and no error generated.
• Tested in CI to verify that buildJavaScriptAndDeps is not run and no error generated.

No manual testing changes envisioned.