Add support for Kotest

[nedtwigg]

If you are only using Kotest with JUnit5, then Selfie will work perfect out of the box with selfie-runner-junit5.

If you want, you can instead use selfie-runner-kotest. This has the slight disadvantage that you will have to register selfie with Kotest, while selfie-runner-junit5 requires no registration. But it has the advantage that it works with Kotlin Multiplatform, so you can take your selfies anywhere that Kotlin and Selfie can run.

Other differences between selfie-runner-kotest and selfie-runner-junit5

• system property selfie.settings -> env SELFIE_SETTINGS

This issue is tracking the completion of the JVM version of selfie-runner-kotest. For JS, see #186. Other platforms are welcome as well.

• create selfie-runner-kotest and undertest-kotest Kotest project setup #185
• copy selfie-runner-junit's Harness class into a HarnessKotest Kotest project setup #185
• copy FSJava and name it FSOkio, implement with okio Implement FSOkio, templated from FSJava #188
• copy SnapshotFileLayoutJUnit and name it SnapshotFileLayoutKotest Implement Kotest SnapshotFileLayout and SelfieSettings #191
• now the tricky part, implement SnapshotStorage, which should work in combination with Kotest's prepareSpec/finalizeSpec/beforeTest/afterTest hooks Bring Kotest support to life #201
• the hardest part is garbage-collecting stale snapshots, leave this out at first Enable GC for Kotest #216

[nedtwigg]

There's two approaches:

• regular JUnit5 runner (Make it easier to mix Kotest and vanilla JUnit5 tests #208)
• kotest-native multiplatform runner (tracked above)

Documenting this will be a bit tricky...

• EDIT: but doable! Update kotest docs #211