[relay-test-utils] createMockEnvironment expects jest to be defined

[rachel-church]

The package.json file of relay-test-utils does not require jest, but attempting to use createMockEnvironment in any test runner except for jest will result in the following error:

ReferenceError: jest is not defined
      at mockDisposableMethod (node_modules/relay-test-utils/lib/RelayModernMockEnvironment.js:40:17)
      at Object.createMockEnvironment (node_modules/relay-test-utils/lib/RelayModernMockEnvironment.js:354:5)

It looks like RelayModernMockEnvironment utilizes jest.fn under the hood to create mock methods on the Environment object.

This issue prevents users from using createMockEnvironment with test runners such as vitest, mocha, jasmine, ava, etc.

Reproduction using mocha: https://glitch.com/edit/#!/frost-tulip-polka