This fixes a few issues:
- strict mode was producing false negatives if multiple query paths
lead to the same element being picked;
- in some cases the number of intermediate items in the list was
exponential and crashed quickly.
What changed:
- `visible` engine is a real engine now;
- `capture` selectors are transformed to `has=` selectors for
easier implementation;
- chained querying switched from a list to a set to avoid
exponential size.
This introduces `locator('div', { has: locator })` syntax that matches elements containing other elements.
Can be used together with `hasText`.
Internally, has selector engine takes an inner selector escaped with double-quotes:
`div >> has="li >> span >> text=Foo" >> span`.
