Support beta status in navigator

[anferbui]

Bug/issue #, if applicable: rdar://155521394

Summary

Currently DocC has some code in RenderIndex to be able to store whether a navigation item is beta or not, but the feature isn't supported yet:

swift-docc/Sources/SwiftDocC/Indexing/RenderIndexJSON/RenderIndex.swift

Lines 257 to 259 in 65aaf92

	// Currently Swift-DocC doesn't support marking a node as beta in the navigation index
	// so we default to `false` here.
	self.isBeta = false

This PR propagates beta information for both render nodes and external render nodes to the navigation index such that we can ultimately encode the information as part of the navigator (i.e. index.json file):

{
  "beta": true,
  "path": "/documentation/mykit/myclass",
  "title": "MyClass",
  "type": "class"
},

Same as in other parts of the codebase, an item is considered to be in beta if all of its platforms are in beta.

Navigator comparison (using swift-docc-render):

Before	After

Dependencies

N/A

Testing

Previewed a custom bundle locally which contained both an external and local link which were both beta.

• Verified that they showed the beta badge in the navigator when using swift-docc-render.
• Verified that the resulting index.json looked as expected

Steps:

1. Use example bundle: Example.docc.zip
2. Set up a link resolver, e.g. using /path/to/swift-docc/bin/test-data-external-resolver and modifying the data as desired
3. Run DOCC_LINK_RESOLVER_EXECUTABLE=/path/to/swift-docc/bin/test-data-external-resolver swift run docc preview --platform name=macOS,version=1.0.0,beta=true --platform name=watchOS,version=2.0.0,beta=true --platform name=tvOS,version=3.0.0,beta=true --platform name=iOS,version=4.0.0,beta=true --platform "name=Mac Catalyst,version=4.0.0,beta=true" --platform name=iPadOS,version=4.0.0,beta=true Example.docc
4. Navigate to http://localhost:8080/documentation/mykit/myotherclass
5. Verify that the index.json is showing the external reference as a node, and that the node has a property beta=true:

    {
      "beta": true,
      "path": "/documentation/mykit/myclass",
      "title": "MyClass",
      "type": "class"
    },
    [...]
    {
      "beta": true,
      "external": true,
      "path": "/resolved/path",
      "title": "Resolved Title",
      "type": "symbol"
   }

Checklist

Make sure you check off the following items. If they cannot be completed, provide a reason.

• Added tests
• Ran the ./bin/test script and it succeeded
• Updated documentation if necessary

[anferbui]

@swift-ci please test

[anferbui]

@swift-ci please test

[sofiaromorales]

@swift-ci please test