There are a few ways for `connect()` to finish:
- `Browser.close()` from the client side.
- Browser on the server side did exit (e.g. crashed).
- Connection was dropped by either of the sides.
We reduce all the cases to the last one by dropping the
connection when client wants calls `Browser.close()` or
server-side browser exits.
In all these cases we should properly cleanup on the server side,
and ensure that all promises reject on the client side.
This changes the root object from RemoteBrowser to Playwright,
similar to local driver connection. This way, any remote connection
gets a Playwright object.
This also starts reusing PlaywrightServer class, and introduces
`cli run-server` hidden command that runs ws server on the
specified port.
Previous structure:
```
RemoteBrowser
- browser (using ConnectedBrowser for remote-specific behavior)
- selectors (special instance for this remote connection)
```
New structure:
```
Playwright
- ...
- selectors (special instance for this remote connection)
- preLaunchedBrowser (using ConnectedBrowser for remote-specific behavior)
```
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.
