Close in favor of #14712 and #14917

Commit Message:
Introduce BufferedIoSocketHandleImpl and UserSpaceFileEventImpl.
This socket handle owns the buffer for itself to read data from and for the peer to write to.
UserSpaceFileEventImpl is the FileEvent this socket could work with.

UserSpaceFileEventImpl provides 3 functions

1. setEnabled(events) declared by FileEvent. The events are registered for callback. Each call detects fired events once, and IO handle will notify the new events in the long run.
2. activate(events). Explicitly activate the events. The above enabling events are not honored.
3. poll(events). It should only be used by IO handle. Unlike activate, poll honors the setEnabled.

The BufferedIoSocketHandleImpl work with ConnectionImpl, and TcpListenerFilter
fdDoNotUse The high level socket option should be intercepted by ConnectionSocket
instead of accessing the fd.

Will provide the example of ConnectionImpl and ConnectionSocket in the next PR.

Additional Description:
Extracted from #13361
Risk Level: Low. Production is not using this socket.
Testing: Added unit test.
Docs Changes: N/A
Release Notes: N/A