[Feature Request] Additional tasks related to the docfx JSON schema

[filzrev]

Summary

docfx JSON Schema definition files are merged to main branch (#9852).

So it can validate JSON/YAML files with following schema URL.

How to test JSON Schema for docfx.
Reference following URLs from editor that support JSON Schema.
And verify validation/intellisense works as expected for JSON/YAML files.

• https://raw.githubusercontent.com/dotnet/docfx/main/schemas/docfx.schema.json
• https://raw.githubusercontent.com/dotnet/docfx/main/schemas/filterconfig.schema.json
• https://raw.githubusercontent.com/dotnet/docfx/main/schemas/toc.schema.json
• https://raw.githubusercontent.com/dotnet/docfx/main/schemas/xrefmap.schema.json

Note

If there is problems. Please report problem this issue or create new issues.

Known issues

• Currently enum is handled as case sensitive.
  (It's because there is no supports for case insensitive enums. and it require additinal regex pattern)
• docfx JSON Schema is using JSONSchema older version draft-07 (It's latest version supported by Visual Studio)
  But "$defs" schemas are used instead of $definition. ($defs is supported after 2019-09 or later)

Remaining tasks
If there are no major problems are reported.
The following tasks will be completed in this issue.

1. Create PR to update SchemaStore's JSON Schema for docfx.
   (SchemaStore's JSON schema files are used if $schema URL is not specified)
2. Add schema validation logics when loading docfx.json config. (For better syntax error reporting)
3. Reorganize Config Reference page contents based on JSON schema.
   4, Add automated tests to verify JSON Schema related changes (By using schema that generated automatically from source code)