Basic @next/font/google integration test (#3170)
This:
* Implements a basic http server to mock returning a stylesheet from the Google Fonts API (**Note**: This importantly does *not* mock returning the font resources themselves, which are currently loaded by the browser. We should implement something to do this when we implement caching arbitrary http resources traced from `url()` and this is no longer loaded by the test browser)
* Adds an integration test that asserts the basic shape of the JS object returned by font functions
* ~Adds an integration test that asserts the browser correctly loads a font for the ascii unicode range, along with the appropriate `font-display`, variant, etc.~ Unfortunately `document.fonts` is not reliable with different font-display loading patterns as any of them can fall back.
As noted, this does not mock responses from Google for the font resources themselves, which are currently loaded by the test browser. This means that we'll be dependent on this external service for passing integration tests until we implement caching of `url()`s in Turbopack. We should monitor the reliability of this test.
