support yaml as format for patterns

[hallvard]

I'm not a bit fan of yaml, but in the case of the patterns, it's IMO preferable, since multi-line code snippets are easier to read and write. I know you are known to dislike and bash yaml, and in general I agree, but in this case ...

E.g. here's part of the the collectors-teeing pattern in yaml:

oldApproach: Two Passes
modernApproach: teeing()
oldCode: |
  long count = items.stream().count();
  double sum = items.stream()
      .mapToDouble(Item::price)
      .sum();
  var result = new Stats(count, sum);
modernCode: |
  var result = items.stream().collect(
      Collectors.teeing(
          Collectors.counting(),
          Collectors.summingDouble(Item::price),
          Stats::new
      )
  );
summary: Compute two aggregations in a single stream pass.
explanation: Collectors.teeing() sends each element to two downstream collectors and merges the results. This avoids streaming the data twice or using a mutable accumulator.
whyModernWins:
  - icon: ⚡
    title: Single pass
    desc: Process the stream once instead of twice.
  - icon: 🧩
    title: Composable
    desc: Combine any two collectors with a merger function.

I will create a PR for this.

[brunoborges]

@hallvard I like the idea of switching to yaml for better source code formatting of code snippets. You think you can draft a program to convert from json to yaml, and verify the generated HTML pages are the same?

[hallvard]

I can try. Hopefully Jackson implements equals on json trees, so I can deserialize json to yaml, read it back in and compare the result.

[hallvard]

I've written a jbang script that reads each original pattern file as a JSON tree, serialises it as YAML, then reads it back as a JSON tree. Comparing them using Jackson's equals implementation shows no difference. The main issues was getting the serialisation options right, with LITERAL_BLOCK_STYLE turned on (to use multi-line strings) and MINIMIZE_QUOTES off (so the jdkVersion field stays a string).

I didn't check the HTML output, since it's a function of the JSON tree. If I fix the ordering issue, the site should be the same.

Should I convert the files or just include the script? Could also use picocli so it can be used as a utility but I think it makes more sense to just convert alle json files.