Update built-in template to incorporate emitter selections

[allenjzhang]

A couple of items for a better user experience in getting started with TypeSpec:

• Update built-in template to incorporate emitter selections
• Decide where the standard catalog of emitters are kept
• Consolidate the schemas
• Add initial simple schema instead of just three import.

[timotheeguerin]

Proposing something like that

In the same way we have the built in template, we define this built in catalog which can be hosted in the compiler

interface BuiltInCatalog {
  libraries: Library[];
  /** List of known emitters */
  emitters: Emitter[];
}

interface LibraryBase {
  name: string; // e.g. @typespec/openapi3
  description: string; // Generate OpenAPI 3 or 3.1 document
  owner: string; // e.g Microsoft .. this is so we can add 3rd party emitters in the future
  homepage: string; // doc url
}

interface Library extends LibraryBase {
  recommendedEmitters?: string[]; // e.g. ['@typespec/openapi3']
}

interface Emitter extends LibraryBase {
  tags: string[]; // e.g. ['openapi3', 'http', 'client', 'server']
  language?: string; // Language emitted by the emitter
}

Difference with current schema

• Rename some properties

  • sourceRepo -> homepage
  • package -> name

• Replace properties with a generic tag: The one layer category is to arbitrary. Some emitter could also technically have multiple categories

  • language
  • category

• Removed requisite and replaced with more generic description for now. This is mostly because this is isn';t anything but documentation for now and if we wanted a more solid prerequisite validation we might want to have it be a more specific format

• Added libraries vs emitters with a way for a library to recommend certain emitters so the init phase can figure it out