Add async-flow test of host vow rejection

[mhofman]

What is the Problem Being Solved?

#9703 was not discovered until we had a test case of an orchestrated contract failure.

We should have caught this in async-flow testing instead.

Description of the Design

Add a test where a host API returns a rejected vow (either immediate or through shortening). The guest does not need to let the error propagate and can handle the rejected guest promise.