Merge meta_schema_types.yaml into source schema

[jack-berg]

Resolves #398. Followup to #411.

Notes:

• Merge all the meta data in meta_schema_types.yaml into source YAML schema files
• Extend make compile-schema to (some of this already exists, but its useful to describe the whole process):
  • While still in source YAML format:
    • Validate all properties have descriptions
    • Validation all enum values have descriptions
    • Validate all types with isSdkExtensionPlugin: true have the same schema
    • Validate that there are no subschemas (i.e. all types are top level - the root of the file - or in $defs)
  • Massage the data and write it to schema_out in .json format
    • Replace all $refs from .yaml source files to .json output files
    • Strip fields which are not part of JSON schema (e.g. isSdkExtensionPlugin)
    • Annotate files with standard metadata fields (e.g. $id, $schema)
• Refactor meta_schema.js tooling to remove everything that interacts with meta_schema_types.yaml, leaving the meta_schema_language_{language}.yaml bits
• Refactor generate-markdown-.js to reflect all these changes

[jack-berg]

Like in #411, the small diff in this file is proof of a strict refactor.

The only changes here are the results of bug fixes which naturally resolved with the simplified organization.

[jack-berg]

This is a stripped down / renamed version of meta-schema.js. No new content here despite how git displays the diff.

[jack-berg]

Will come back and fix this once things stabilize. Just too much in flux right now for it to be worth documenting the details at intermediate steps.