Add WithToken variants to Send/Recv/Infeed/Outfeed ops in XLA builder.

In HLO side-effecting ops now take and produce a token-shaped value used for ordering. This CL exposes the tokens in the XLA builder interface by adding builder variants suffixed with "WithToken". These variants have an extra token-shaped operand and produce a token, sometimes as a element in the tuple-shaped output of the op.

Also, at the HLO level, add new method CreateToken for creating an instruction which produces token-shaped value out of thin air using an AfterAll instruction. This is explicitly broken out from CreateAfterAll to facilitate remove of zero-operand AfterAll instructions (b/110532604).

PiperOrigin-RevId: 203834271