Convert createWasm async/await where possible

[sbc100]

The advantage if using await in the cases where we can is that it avoids the generation or wrapper function for each export.

So instead of

var wasmExport = createWasm(); // returns empty object
...
var malloc = (..) => (malloc = wasmExports['malloc'])(..);

We can just generate:

var wasmExport = await createWasm(); // returns actual exports
...
var malloc = wasmExports['malloc'];

This only currently works in MODULARIZE mode where the code is running inside a factory function. Otherwise it would end up using top-level-await.

One wrinkle here is that this is not currently supported when closure is enabled because we run closure only on the contents of the factory function so closure ends up seeing this as a top level await when its not.

There are two minor observable effects of this change:

1. In MODULARIZE mode its no longer possible to call new Foo() with factory function. We already added a warning for this debug builds in Assert if MODULARIZE factory function is used with new. #23210.
2. Because we now can await for createWasm to return, the run method can run on first call, which means it runs main on first call, which means main will now run before postjs code, just like it would with sync instantiation.