Fix for race condition when using sha256 on IE11

[stevehobbsdev]

Description

This PR fixes an issue with resolving SHA256 operations in IE11.

msCrypto (IE11) uses the old spec, which is not Promise based. Instead of returning a promise, it returns a CryptoOperation
with a result property in it.

As a result, the various events need to be handled in the event that we're working in IE11 (hence the msCrypto check). These events just call resolve or reject depending on the handler.

The sha256 function essentially now has two clear paths depending on IE11 vs. not-IE11 - either return the promise from the browser's crypto API, or return a new promise which is resolved or rejected based on the events raised by msCrypto.

References

CryptoOperation reference: https://msdn.microsoft.com/en-us/expression/dn904640(v=vs.71)

Testing

• This change adds test coverage for new/changed/fixed functionality

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not master