[embind] Export embind exports as ESM exports for MODULARIZE=instance.

[brendandahl]

Using the embind AOT mode we can generate a list of all the embind bindings and export them as ES module exports.

[sbc100]

To be clear this only works in AOT mode? What happens in non-AOT mode?

[brendandahl]

To be clear this only works in AOT mode? What happens in non-AOT mode?

In non-aot mode, the user would have to get the bindings off the module object from init. e.g.

const module = await init();
module.foo();

We could require that modularize instance + embind only works with embind_aot, or enable embind_aot in instance mode by default. I lean towards the latter.

[brendandahl]

I've updated this to work with the changes with exp__ being removed. I was hoping to use the emscripten.py code for the exports, but unfortunately phase_embind_aot runs after emscript.