fix(http-server-csharp): fix model file name when @friendlyName contains unresolved template placeholders

[Copilot]

When @friendlyName stores a format string with {paramName} placeholders that weren't substituted (e.g. {name}TagsUpdate), the generated file was named {name}TagsUpdate.cs while the class inside was correctly named NameTagsUpdate — a discrepancy caused by the class name going through pascalCase() (which treats {/} as word separators) while the file path used the raw string.

Changes

• src/components/models/model-helpers.ts — In getModelEmitName, sanitize the @friendlyName return value by replacing {paramName} placeholders with their PascalCase equivalents before using the name as a file path:

  return friendlyName.replace(/\{(\w+)\}/g, (_, n) => n.charAt(0).toUpperCase() + n.slice(1));

  {name}TagsUpdate → NameTagsUpdate.cs, matching the emitted class name.

• test/generation.test.ts — Regression test: verifies that a model decorated with @friendlyName("{name}TagsUpdate") produces NameTagsUpdate.cs with no literal {name} in the output path.

• Fixes [Bug]: http-server-csharp: Generated model file for NameTagsUpdate is {name}TagsUpdate.cs #11454

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commit: 6f90881

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• ✅ @typespec/compiler

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@typespec/compiler - fix ✏️

Fix decorators running with unresolved template parameters when a decorated template is used as a template parameter default of an operation (e.g. op foo<Resource, Properties = Decorated<Resource>>(...), the ARM TagsUpdateModel<Resource> pattern). Operations now enter the template declaration scope before resolving template parameter defaults, so decorators on those defaults are no longer executed with the still-unresolved template parameter. This matches the existing behavior for models and interfaces.

@typespec/http-server-csharp - fix ✏️

Fix model file name for @friendlyName ARM-style template patterns (e.g. @friendlyName("{name}TagsUpdate", Resource) on TagsUpdate<Resource>). The instantiation now correctly receives the substituted name (e.g. FooResourceTagsUpdate.cs) from the compiler.

[timotheeguerin]

Superseded by #11477, which contains only the root-cause compiler fix (operations now enter the template declaration scope before resolving template parameter defaults, so decorators no longer run with unresolved template parameters). This PR had diverged from its original purpose across several earlier attempts, so closing in favor of the clean replacement.