[XLA] Redesign: add the rest of client-service interfaces.

The basic idea is, on the client side, for each public method that has a Computation parameter, add an overload with XlaCompuation. If such method needs to call the service side, add corresponding service interfaces.

Also make XlaCompuation::GetProgramShape return StatusOr, to be consistent with the Computation class.

PiperOrigin-RevId: 190822601