Implement SnapshotValueReader

[nedtwigg]

Implementing SnapshotValueReader is the first step. One key trick:

• We are using Kotlin Multiplatform, and unfortunately we are currently hitting a known bug which requires us to use the alpha-quality K2 compiler.
• If gradlew test is failing, try a gradlew clean then try again. This is because of K2.

[jknack]

@nedtwigg should I merge this? or work in the feature branch?

[nedtwigg]

Work in this feature branch

[jknack]

@nedtwigg here is. I took me a bit I have to learn/read a bit about KMM and also struggling with IDEA to run tests.

Make LineReader.readLine nullable to follow the JVM version.

[nedtwigg]

Looks great at first glance! I'll take a look later tonight and then point you at the next task on this project.

[nedtwigg]

@jknack an excellent start! I did a few things in the commits above:

• I refactored ArrayMap a bit so we can disable the experimental K2 parser, IDE tests should now be reliable
• I fixed some things
• I broke some things on purpose

My advice is:

• Look quickly at each commit I pushed above, one by one
• Implement the functionality needed for skipValues to pass, don't worry if some of the other tests break
• Then fix the other tests

[jknack]

@nedtwigg pushed a new commit. I left one question about body escape

[nedtwigg]

Excellent, you did the hard part, I think the commit above explains the tiny bit leftover. The purpose of the weird escape stuff is just:

• literally anything can be a "name" (no dissallowed characters)
• literally anything can be a "value" (no dissallowed characters)
• names and values will always round-trip perfectly with no confusion or changes (except we don't preserve \r\n vs \n)
• the snapshot files look human readable and have as little escaping as possible, but some is needed to ensure the points above

This PR is done now. I am going to:

• open and then merge a PR which does some renaming / refactoring
• open a new PR for you to implement for the next step

I will complete this later this evening.