Asyncify "OOM" leaves broken state

Right now, emitted Asyncify unwind/rewind mechanisms always stores all the variables while unwinding, and only performs bound checks in points like asyncify_stop_unwind when memory outside of bounds is already corrupted.

This leaves module in a broken state: even if you catch & handle the original error, calling into other exports after this point can result in all sorts of broken behaviour.

A better solution would be to perform bound checks right before storing the locals - their size is known in advance, so such condition should be fairly simple and wouldn't add any noticeable overhead, but would improve reliability a lot.

cc @kripken thoughts?

Start by tracing the emitted Asyncify unwind/rewind mechanisms and the existing bound checks at points such as asyncify_stop_unwind. Verify how much local storage is required before unwinding, then confirm that an out-of-bounds condition is handled before locals are stored and that the module remains usable after the original error is caught.