[compiler] Identifier interpolation

[witemple-msft]

WIP

This PR enables interpolation of string values into identifiers in many cases, reusing the existing syntax for keyword escapes.

• Type declaration identifiers: model, union, enum, interface, etc. (with the limitation that these are not possible to reference by identifier, but they can still be declared. But NOT namespaces as this is just too fraught.
• Member identifiers: interface operations, model properties, enum members.

⚠️ This was 100% generated by the copilot CLI as an experiment.

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npm i https://pkg.pr.new/microsoft/typespec/@typespec/compiler@9791

commit: 4cf581d

[github-actions]

All changed packages have been documented.

• ✅ @typespec/compiler

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@typespec/compiler - feature ✏️

Added the ability to interpolate identifiers in most positions (model, property, enum, union, scalar, operation names, etc.). To compute an identifier, use backticks as if creating a templated string type (e.g. const v = "Model"; model \My${v} { ... }).

[azure-sdk]

You can try these changes here

🛝 Playground	🌐 Website	🛝 VSCode Extension

[witemple-msft]

I think I don't like this way of implementing this. It seems too fragile to allow this anywhere we call parseIdentifier... I think it would be better to have a parseIdentifierOrInterpolated and only call that from syntactic positions where it should be allowed.

[witemple-msft]

On the other hand diagnostic behavior is probably better this way, since we get a clean "interpolation not allowed here" error instead of "unexpected token"...