instance{WebAssembly.Instance}
Attempt to initialize instance as a WASI reactor by invoking its
_initialize() export, if it is present. If instance contains a _start()
export, then an exception is thrown.
initialize() requires that instance exports a [WebAssembly.Memory][] named
memory. If instance does not have a memory export an exception is thrown.
If initialize() is called more than once, an exception is thrown.
