Token APIs have confusing names

[davidchisnall]

A bunch of the APIs have obj in the middle, which violates our 'no abbreviations' policy. I'm not convinced that 'token' is actually the right name for this at all (bikeshedding welcome).

We can probably also remove token_sealed_unsealed_alloc. This has to return one result indirectly and so introduces some pain in the ABI. It was added because token_obj_unseal was a second cross-compartment call, but now it is a (fast) call into the token library and so it may be simpler to just return the sealed object and rely on the caller to unseal it.

[nwf]

Whatever names we end up with, we should probably also rename SKeyStruct/SObjStruct/SKey/SObj.