Move examples tests to their own workspace (#4630)
This PR:
- Makes `examples_tests` an official workspace in
`turborepo-tests/examples`
- Extracts some helpers from `turborepo-tests/integration` into their
own workspace
- This will cause examples tests to run when those helpers change,
avoiding issues like #4626.
- Make `examples/` a workspace, and sets up a package.json dependency,
so that when examples change, examples_tests are also invalidated. (Note
that this doesn't affect when CI runs since that's configured in Github
Actions workflow configs)
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Co-authored-by: Nathan Hammond <nathan.hammond@vercel.com>