EMBIND_AOT should AOT method callers

We have `emval_methodCallers` mechanism used for `foo()` and `foo.call<...>(...)` on `emscripten::val` instances here: https://github.com/emscripten-core/emscripten/blob/2fe9aeb84fb2b3f4462ecd6a8d7f156c06349312/src/lib/libemval.js#L284-L352

Right now it either constructs a JS function from strings on the fly, or uses a slower mechanism with looking up all the types on each invocation.

As far as I can tell, it should be fairly straightforward to add it to the `EMBIND_AOT` processing so that specialized function is generated during compile-time and then reused. cc @brendandahl