Add Support For Uri Template Path Expansion

[jorgerangel-msft]

Follow up to #5396. Typespec added uri template support which allows for path expansion for path parameters. The emitter + MGC currently only support exploding query parameters but a design should be considered to support the same for path expansion.

Typespec ref: #3736 (comment)

[JoshLove-msft]

This is covered by existing cadl-ranch scenarios - need to link to the existing scenarios - under Routes.

[jorgerangel-msft]

Cadl ranch scenario: https://github.com/Azure/cadl-ranch/blob/main/packages/cadl-ranch-specs/http/routes/main.tsp

[JoshLove-msft]

There isn't BCL support for Uri Template as far as we know - #3736 (comment). We would need BCL support for this as we won't be rolling our own Uri Template parser.

[JoshLove-msft]

The only part that is a GA requirement is explode and allowReserved which we already support.

[JoshLove-msft]

Ideally, BCL would provide support for this. We should start an email thread on this topic.

[JoshLove-msft]

The plan is that this should be supported in TCGC so that languages can avoid taking runtime dependencies on uri template libraries and so that the logic is consistent across languages. TCGC would need to parse the URI template into an AST that is passed back to all of the emitters.

[JoshLove-msft]

Basic parameter replacement can be supported in the meantime, e.g.

@server(    
  "https://{region}.codesigning.azure.net/",    
  "Sign and retrieve relevant information pertaining signing process.",    
  {    
    @doc("The Azure region wherein requests for signing will be sent.")    
    region: string,    
  }

should be able to be generated. Currently this crashes.