Add RpcTargetMetadata generation from ITypeShape

[AArnott]

This allows for creating RPC targets for any type for which a PolyType shape is available, such that it's safe in a trimmed app without a dynamic runtime (e.g. NativeAOT).

This is an important prerequisite for the NerdbankMessagePackFormatter to be able to support RPC general marshable objects, as they become RPC targets in an almost unpredictable fashion.

[Copilot]

Pull Request Overview

This PR adds support for generating RpcTargetMetadata from ITypeShape objects, enabling RPC target creation for types with PolyType shapes. This functionality is essential for supporting trimmed applications and NativeAOT scenarios where dynamic runtime reflection is not available.

Key changes:

• Adds new FromShape methods to generate RPC metadata from type shapes
• Refactors TargetMethodMetadata to support shape-based construction
• Updates method references from Method to MethodInfo for clarity

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
RpcTargetMetadata.cs	Core implementation of shape-based metadata generation with new FromShape methods
RpcTargetMetadataTests.cs	Test coverage for the new shape-based functionality
TargetMethod.cs	Updates method property references to use new MethodInfo property name
RpcTargetInfo.cs	Updates method creation call to pass null shape parameter
ProxyGeneration.cs	Updates method property reference to use new MethodInfo property name
PublicAPI.*.txt	API surface updates for the new methods and property changes
StreamJsonRpc.csproj	Enables format methods for embedded resources
Resources.resx	Adds error message for missing AttributeProvider
Directory.Packages.props	Adds PolyType package dependency

---

_{You can also share your feedback on Copilot code review for a chance to win a $100 gift card. Take the survey.}