This changes quoted text selector like `text="Foo Bar"` to perform
normalized whitespace match.
Most of the time users want to match some string visible on the page,
and that always means normalized whitespace.
We keep the case sensitivity and full-string vs substring difference
between quoted and unquoted matches.
We now default to `text` that does substring case-insensitive match
with normalized whitespace. `text-is` matches the whole string.
`matches-text` is renamed to `text-matches`.
This is a large rework of selectors:
- Each BrowserContext now has a separate Selectors instance that has its own registrations.
Most of them share a single sharedSelectors instance, but contexts created for a connected
browser have their own instance.
- Connected browser now gets a RemoteBrowser object that encapsulates Selectors and Browser.
This Selectors object is registered with the api selectors.
- Public selectors.register api iterates over all registered Selectors channels
and registers in each of them.
- createSelector testing method migrated to ElementHandle._createSelectorForTest.
