Refactor JS API amalgamation such that the bootstrapping/configuration is deferred until the whole amalgamation is available, to facilitate providing clients with a way to initialize the API with their own config (noting that we're still one small level of refactoring away from being able to actually do that).

FossilOrigin-Name: 9dbe9a6aecec43b51057375ef1d2d632db0d17eac8b7552c20cc91fc2f1a55d1