fix(jest-jasmine2): point to inline snapshot documentation if prettier is unavailable

[theneva]

Summary

Use of inline snapshots requires the project to expose prettier. If prettier is not available, Jest currently fails with a message that does not indicate any required action on the user's part:

These changes append a brief message and a link to the inline snapshot docs to that message (I've since changed prettier to Prettier in the message):

Test plan

To be honest, I have no idea how to write a test for this. To verify the changes manually, I ended up removing the prettier dependency from a test project (https://github.com/theneva/post-utils), and:

1. Linked jest-jasmine2 into the test project
2. Made my changes to jest
3. Built jest
4. rm -rf node_modules/prettier in jest to prevent it being accidentally made available through the linked dependency
5. Ran yarn jest in the test project

If it makes sense to write an integration test for this, I'd be happy to do so if someone points me in the right direction 😄

[SimenB]

Thanks!

Mind adding a test? Integration test is fine (if it's possible to make the module not possible to find).

This also needs to update for jest-circus

[SimenB]

@theneva mind rebasing this and fixing it for circus as well? As for a test, I think the easiest might be to do prettierPath: 'some-module-that-does-not-exist' in an integration test

[SimenB]

@theneva ping, pls rebase this

[thymikee]

Closing, since this will soon be fixed by #7792. Thanks!

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