Replace crypto-hash with a custom hashing function in tests

[hwillson]

It looks like some combination of the changes in #9928 and #9942 exposed a long running issue caused by using crypto-hash in our @apollo/client/link/persisted-queries tests. crypto-hash spawns a thread the first time it's called, and keeps that thread alive until the end of program execution, if worker threads are available (which they are for our tests since they're running in CI via Node). Unfortunately there appears to be some kind of a race condition between crypto-hash unrefing its worker and Jest reporting a successful test suite exit, which leads to Jest reporting the following (which is seen by running jest with the --detectOpenHandles setting enabled):

Jest has detected the following X open handles potentially keeping Jest from exiting:

This then appears to be leading to failed tests in CI.

We can look further into what's causing this race condition between crypto-hash and Jest, but just dropping the use of crypto-hash is likely a faster solution. We just need to verify that a hashing function can be successfully set and used with the persisted queries link, which means we can replace crypto-hash with our own simple function that doesn't use worker threads. This commit does just that by introducing a super simple custom sha256 function that leverages Node crypto, and uses it instead.

Fixes #9982

[hwillson]

Note that this isn't ready for review yet - this fixes the Jest open handle issue but there is more to do.

[hwillson]

Hmm - the initial changes in this PR fix one problem (that crypto-hash was keeping a worker thread open), but Jest is still hanging off and on. This appears to be caused by our new use of Jest's projects feature along with leveraging multiple Jest workers. Something is hanging and Jest can't properly exit because of it. Running all our of tests serially fixes the issue (using Jest's runInBand feature), but this slows our tests down a bit. Still, we might want to get this in for now to at least get our tests back to passing reliably. We can then continue to look into what's causing the hanging.

Another option is to keep the Jest workers enabled and forceExit Jest, but leaving whatever Jest is having a hard time with open could cause harder to troubleshoot tests errors in the future.