Links to JSON schema files from AsciiDoc files

[javagl]

Right now, there are some links from ADOC files directly to JSON schema files in the GitHub repo, for example,

The common structure of metadata entities that appear in a tileset is defined 
in link:https://github.com/CesiumGS/3d-tiles/tree/draft-1.1/specification/schema/metadataEntity.schema.json[metadataEntity.schema.json].

The reason is that it should be possible to browse to these files, from the GitHub preview of the ADOC file. But one could make a case that these links should point to the "JSON Schema Reference" in the single-page HTML version.

In any case, we should identify these links, and maybe try to make them point to

• the actual JSON file on GitHub
• the inlined JSON in the single-page HTML

consistently in the specification. (This should be possible using the ifdef-trickery that is already used for other links - it may be a bit clumsy, but there should not be sooo many of these links, and therefore, it could be manageable)