Bump frontend-build to v14

[bradenmacdonald]

As a developer, I would like to use TypeScript when writing code for frontend-app-course authoring.

That requires frontend-build 14, which already works with this repo (no changes required) - but a bunch of peerDependencies issues need to be resolved, so a few other packages need to be bumped at the same time:

• frontend-platform v8
• react-unit-test-utils (PR)
• frontend-lib-content-components needs to be updated to support platform v8 and build v14 (PR), then bumped in this repo
• possibly others?