Add expression converter for sample generation

[radhgupta]

What

Adds ExampleValueExpressionBuilder — converts InputExampleValue + CSharpType → ValueExpression (C# AST nodes). Also adds ExampleParameterValue bridge type. This is M2 of the test/sample generation feature.

How it works

The builder dispatches on CSharpType to produce the correct C# expression:

Input	Output
"hello" + string	Literal("hello")
"73f4..." + Guid	Guid.Parse("73f4...")
"http://..." + Uri	new Uri("http://...")
1234 + int	Literal(1234)
{...} + BinaryData	BinaryData.FromObjectAsJson(new { ... })
[...] + IList<T>	new T[] { ... }
"Monday" + DayOfWeek	DayOfWeek.Monday

ExampleParameterValue supports two modes — pre-built Expression (for known params like credentials) or raw Value (for spec-provided data needing conversion).

Changes

• New: ClientModel/src/Providers/Samples/ExampleValueExpressionBuilder.cs
• New: ClientModel/src/Providers/Samples/ExampleParameterValue.cs
• New: ClientModel/test/Providers/Samples/ExampleValueExpressionBuilderTests.cs (52 tests)
• Modified: Input/src/Properties/AssemblyInfo.cs — added InternalsVisibleTo for Generator and ClientModel projects to access internal example subtypes (InputExampleRawValue, etc.)

Design doc

https://gist.github.com/radhgupta/9fee69190f1ac2252a88dd88f99de327

[pkg-pr-new]

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npm i https://pkg.pr.new/@typespec/http-client-csharp@10393

commit: 8368f04

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