WebAssembly module: all problem types, sessions and a Web Worker

[fontanf]

Stacked on #632: this PR's diff only shows the second step. Once #632 is merged, GitHub retargets it to master.

Changes

All problem types: solve and Session accept rectangleguillotine, rectangle, box, boxstacks, onedimensional and irregular, through one generic template over the six namespaces.

Session: solving without blocking.

const session = new module.Session();
session.start("rectangle", instanceJson, JSON.stringify({optimization_mode: "anytime"}));
// Then, periodically:
const {solutions, done, result} = JSON.parse(session.poll());
// ...
session.stop();    // The optimization ends with its best solution.
session.delete();

• start runs the optimization in a thread of its own and returns immediately.
• poll returns the updates since the previous call. There's an update each time the best solution or a bound improves, so an update may have no new solution, e.g. the bound found before any solution. At the end, poll also returns the result.
• stop stops the optimization. With timer.add_end_boolean, as in the Python bindings.
• Updates are produced on the algorithms' threads, which can't call JavaScript functions owned by the thread holding the session. So they're queued under a mutex and returned by poll. The calling thread never blocks.

Web Worker: wasm/js/packingsolver_worker.js runs a session and posts the updates to the page.

Direction	Messages
to the worker	{type: "solve", problemType, instance, parameters}, {type: "stop"}
from the worker	{type: "ready"}, {type: "solution", output, certificate}, {type: "done", output, certificate}, {type: "error", error}

It's a classic worker in the browser. It also runs in Node with worker_threads, which is how it's tested.

Size: with the six types, the module is 7.4 MB, 2.4 MB gzipped.

Testing

node --test wasm/tests/: 31 tests, all passing in three consecutive runs. None uses a time limit.

• solve, each problem type in not-anytime and not-anytime-sequential modes. Also the rectangle tests of Add a WebAssembly module #632: anytime mode on an instance proven optimal, the README example in the three non-anytime modes, and the error cases.
• Session:
  • anytime mode on an instance proven optimal;
  • each problem type in anytime mode, stopped at the first solution;
  • stopping the README example, whose objective has no bound, so it only ends when stopped;
  • errors, and starting a session twice.
• Web Worker: updates, stop and result; errors.

Not tested in a browser yet: that needs a page served with the headers enabling SharedArrayBuffer, the next step.