Migrate format unit tests to cram

[davesnx]

This PR moves all formatTests/unit into refmt_tests/. Added the test suite as part of https://github.com/reasonml/reason/pull/2687.

It doesn't delete the tests from formatTest and it will be done in a further PR.

Part of this PR includes a README with the minimum explanation to run tests, you can take a look under refmt_test/README.md

This PR is spiritually the same as https://github.com/reasonml/reason/pull/2616 by me and https://github.com/reasonml/reason/pull/2454 by @sync (btw, the funny fact here is that it was my first attempt to contribute to reasonml/reason and failed because of the complexity around rely/esy/opam/Azure/CircleCI). In this case, I have already ensure the CI works with one single test https://github.com/reasonml/reason/pull/2687 and we can do the migration progressively.

Why

• ./test.sh it served its purpose, but it's hard to maintain: Hard to update, hard to understand which files depend on which commands, why some stuff is there in the first place.
• cram tests force to organize the tests around folders and it's explicit commands, and helps to keep tests small which isn't the case for most current snapshots.
• With the possibility to have all stages of testing on the same input.
• cram tests are fast
• They run in watch mode, and only build refmt once.
• cram makes it easy to generate snapshots (something we had to manually do) and diff snapshots for us with meaningful error messages
• Much easier and less error-prone to add new tests/update present.

Example of a faiing test in CI

This is an example (on purpose) of tests failing:

• CircleCI: https://app.circleci.com/pipelines/github/reasonml/reason/480/workflows/d0b979fc-4da1-4af8-be8e-08a871f4a2b8/jobs/19945
• Azure DevOps: https://dev.azure.com/reasonml/reason/_build/results?buildId=897&view=logs&jobId=12000c61-2a71-5cf0-ffc6-523f919554c5&j=12000c61-2a71-5cf0-ffc6-523f919554c5&t=9e6f41fb-82cb-5a47-d081-0e6923424005

Process

The migration path I took:

1. Move input/XXXX as XXXX/input.(re|rei|ml)
2. Move output/XXXX as XXXX/run.t
3. Add 2 spaces to all lines
4. Prefix with a comment "Format XXXX" and the refmt call

Some tests are renamed

There were a few tests with same name but different extensions:

• formatTest/unit/*/wrappingTest.re -> refmt_test/wrapping-re.t
• formatTest/unit_test/*/wrappingTest.rei -> refmt_test/wrapping-rei.t
• formatTest/unit/*/whitespace.re -> refmt_test/whitespace-re.t
• formatTest/unit_test/*/whitespace.rei -> refmt_test/whitespace-rei.t

A generic test called formatTest/unit/*/syntax.re and formatTest/unit/*/syntax.rei got renamed to refmt_test/general-syntax-re and refmt_test/general-syntax-rei