Previously a heuristic based on function naming was used to determine
whether `Injector` should construct objects with `new` or not. This is
brittle because compiler transforms may alter function names (eg. terser
removes them by default).

This commit re-works the API so that the caller explicitly indicates how
the object should be created (the "provider" to use). As a convenience
if a function is passed it is assumed to be a class.

```
// Register a class.
register("anObject", SomeClass);
register("anObject", { class: SomeClass });

// Register a factory.
register("anObject", { factory: makeMeAnObject });

// Register a plain value.
register("anObject", { value: "foobar" });
```