[tcgc] reorganize tcgc staff

[tadelesh]

1. reorder clients, enums, models and unions. it will all follow the client's declaration sequence (client from namespace first, then client from interface)
2. report warning for multiple @service and fall back to the first one
3. reorganize the validation code
4. reorganize the type graph creation code
5. add client initialization author doc
6. add package author doc

TODO: rewrite all the docs and add more validation for methods, types, and operations

resolve: #2299
resolve: #1766

[azure-sdk]

All changed packages have been documented.

• ✅ @azure-tools/typespec-client-generator-core

Show changes

@azure-tools/typespec-client-generator-core - breaking ✏️

Reorder clients, enums, models and unions.

@azure-tools/typespec-client-generator-core - feature ✏️

Report warning for multiple @service and fall back to the first one.

[azure-sdk]

You can try these changes here

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