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)
```
- Allow specifying which browsers to install. This comes handy in playwright-cli.
- Print "npx playwright" as a tool name in help messages, instead of "cli".
