Proposal: Add async API

[Sayan751]

Currently, the API is exclusively synchronous. An asynchronous API would be easier when waiting for a particular state in tests.

• await spy.isCalledAsync(methodName, [count], [timeout]);
• await spy.isCalledWithAsync(methodName, argList, [options]);
  • argList can be either [arg_1, ..., arg_n] for a single call or [[arg_1_1, ..., arg_1_n], ..., [arg_m_1, ..., arg_m_n]] for multiple calls.
  • options can have the following properties:
    • orderInsensitive: when set to true then the order of the argList does not matter.
    • isSet: when set to true, then the argList is considered as a set.
    • index: when set, then the argList is matched against a particular invocation of the method, indicated by the given index.
    • timeout: if the assertion fails, when it cannot be resolved under the given timeout.