Remove the ServiceApi and ObjectApi abstractions

[igalshilman]

This commit removes the previously introduced ServiceApi and ObjectApi types. With this commit applied, we no longer need a special concept, but simply import the typeof the Service/Object.

a.ts:

const greeter = restate.service("greeter", {
  greet: async (ctx: restate.Context, name: string) => {
    return message;
  },

});

export type GreeterService = typeof greeter;

b.ts

import type {GreeterService} from 'a.ts';
...
const Greeter: GreeterService = { path: "greeter" };
ctx.service(Greeter).greet("hello");
...