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This runs Jest on the outputs of the built test files and reports the results of the test execution. It depends on `jest` and `jest-environment-jsdom` as optional peer deps validated in the builder, so there isn't a strict dependency on Jest for applications which don't use it.
Jest exports a `runJest()` function, however it can't be used directly because we need to opt-in to `--experimental-vm-modules` in ordre to run Jest on native ESM JavaScript as produced by `browser-esbuild`. This means we need a Node subprocess in order to add this flag, because the `ng` command cannot add a Node flag to its own current execution. This unfortunately means we can't just `import * as jest from 'jest';` or even `require.resolve('jest')` because that returns the library entry point exporting `runJest()`, rather than a script which actually runs Jest on load. Fortunately, Jest exports it's `node_modules/.bin/jest` entry point from its `package.json` under `jest/bin/jest`, so we `require.resolve()` _that_ to get the path to the correct file.
Executing Jest is fairly straightforward, running on the output of the `browser-esbuild` execution with outputs streamed to the console. We opted to use JSDom over Domino in order to align with the existing Jest ecosystem.