SwaggerEditor@next: add validation errors for unsupported YAML tags

[ponelat]

Is your feature request related to a problem?

Using custom YAML tags is unsupported by OpenAPI specifications, and the Editor does not warn authors about this.

Describe the solution you'd like

Validation errors when trying to use a non-supported YAML tag.

Example

openapi: 3.1.0

info:
  version: '1.0.0'
  description: binary
  title: Binary

components:
  schemas:
    Binary:
      type: string
      description: Example binary content
      format: binary
      example: !!binary |-  
        - tag !<tag:yaml.org,2002:binary>
          c3dhZ2dlcg== # Base64 encoded