python SnapshotFile

[Trickybrain]

To take step in diffplug#7

SnapshotFile
https://github.com/diffplug/selfie-python-wip/blob/2aededc364606e8dcd3c3f69669cb415a0b34b2f/jvm/selfie-lib/src/commonMain/kotlin/com/diffplug/selfie/SnapshotFile.kt#L137-L241

SnapshotFile Test
https://github.com/diffplug/selfie-python-wip/blob/2aededc364606e8dcd3c3f69669cb415a0b34b2f/jvm/selfie-lib/src/jvmTest/kotlin/com/diffplug/selfie/SnapshotFileTest.kt#L21-L94

[nedtwigg]

@Trickybrain great work! Looks like you've got the whole snapshot file epic completed! A few improvements which will be important to make the rest work:

• Snapshot.facetData should be an ArrayMap[String, SnapshotValue]
• SnapshotFile.snapshots should be an ArrayMap[String, Snapshot]

It needs to be ArrayMap because ArrayMap has a special sort-order for strings, which makes the / character the lowest possible character.

Static types should make this much easier than without them :)

[nedtwigg]

• Fixed by Fix the python landing page (but keep hidden) - blocked #334