This patch moves fixtures.js to base.fixtures.ts that sits next to tests. All tests get an extra import to get the base fixtures (both types and implementations).
We now query selector and take textContent synchronously. This
avoids any issues with async processing: node being recycled,
detached, etc.
More methods will follow with the same atomic pattern.
Drive-by: fixed selector engine names being sometimes case-sensitive
and sometimes not.
