Bump C# emitter dependencies to TypeSpec 1.9.0

[Copilot]

Updates TypeSpec compiler and related packages to 1.9.0, along with corresponding TCGC and spec package versions.

Dependency Updates

• TypeSpec core packages: 1.8.0 → 1.9.0
  • @typespec/compiler, @typespec/http, @typespec/openapi, @typespec/json-schema
• TypeSpec standard libraries: 0.78.0 → 0.79.0
  • @typespec/rest, @typespec/streams, @typespec/versioning, @typespec/xml, @typespec/library-linter
• TCGC: 0.64.4 → 0.65.0
• Spec packages: Updated to versions compatible with 1.9.0
  • @azure-tools/azure-http-specs: 0.1.0-alpha.35 → 0.1.0-alpha.37
  • @typespec/http-specs: 0.1.0-alpha.30 → 0.1.0-alpha.32
  • @typespec/spector: 0.1.0-alpha.20 → 0.1.0-alpha.23
• New peer dependency: @typespec/sse@0.79.0

Type System Changes

Updated InputDateTimeType and InputDurationType to match TCGC 0.65.0's broadened encode property:

// Before: encode: DateTimeKnownEncoding
// After:
encode: DateTimeKnownEncoding | string

Runtime Fix

Fixed deserialization crash for string-based enum arrays. Custom enum types don't expose FrameworkType, so use PropertyInitializationType instead:

// Before: New.Instance(typeof(List<>).MakeGenericType(elementType.FrameworkType), ...)
// After:
New.Instance(propertyType.PropertyInitializationType, selectExpression)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Bump C# emitter dependencies</issue_title>
<issue_description>We should bump to the new typespec/compiler version 1.9.0 and all the other new versions for typespec packages.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Bump C# emitter dependencies #9674

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[JoshLove-msft]

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