Enable RPC marshalable objects in NerdbankMessagePackFormatter

[AArnott]

This was particularly challenging because [RpcMarshalable] interfaces can also prescribe 'optional' interfaces which may or may not be implemented by the marshaled object, and this information must be available on the receiving end. We transmit this information (before this PR), but on the receiving end, we would previously emit a dynamic proxy that implements exactly that set of interfaces. To preserve the NativeAOT readiness of NerdbankMessagePackFormatter though, we need to use source-generated proxies. A marshalable interface with 8 optional additional interfaces would require 256 proxies to be source generated to have every possible combination, which is ludicrous. Instead, we emit a proxy with just the core interface and another with all the optional interfaces. Receivers who want to test whether an interface is actually available on the remoted object should use the new Is and As<T> methods, which the proxies can respond to based on intended implementation.

This was also tricky because these optional interfaces may overlap one another in method name or in base types. Since each optional interface has a number prefixed to its method names, we have to be intentional about which prefix to use for a given method that may be reachable from multiple optional interfaces. This unfortunately wasn't thoroughly thought through for dynamic proxies, so for source generated ones we harden it, at the downside of not being entirely compatible with dynamic proxies. But this is a corner case which I suppose no one has hit yet anyway.

I made a design choice to keep the source generated code for proxies very much ignorant as to all the policies around renaming methods. This is because it's not simple, and might evolve over time. But we can't simply evolve all source generated proxies that are compiled into other assemblies, so instead we just have them call into our library for the method transformations at runtime. That has a small runtime cost, but is probably worth retaining the ability to service any bugs we discover later.

• Emit source generated proxies for [RpcMarshalable] interfaces and their optional interfaces.
• Add new IClientProxy interface that can be used to type check proxies that may implement too many interfaces. This is deliberately separated from the pre-existing IJsonRpcClientProxy so that RPC isn't relevant, allowing Microsoft.ServiceHub.Framework-generated local proxies to also implement it in a similar way, such that brokered service clients need not know whether RPC is involved to do a proper type check.
• Add several new diagnostic analyzers
• Bump Nerdbank.MessagePack to its latest prerelease version

[Copilot]

Pull Request Overview

This PR enables RPC marshalable objects in the NerdbankMessagePackFormatter by implementing source-generated proxies and improving type safety for NativeAOT compatibility.

• Adds source-generated proxy support for [RpcMarshalable] interfaces with optional interfaces
• Introduces new IClientProxy interface for better type checking
• Integrates PolyType for shape generation while maintaining runtime flexibility for method transformations

Reviewed Changes

Copilot reviewed 125 out of 125 changed files in this pull request and generated 17 comments.

Show a summary per file

File	Description
test/StreamJsonRpc.Tests/Usings.cs	Adds global using for PolyType
test/StreamJsonRpc.Tests/ObserverMarshalingTests.cs	Adds GenerateShape attribute for method shapes
test/StreamJsonRpc.Tests/ObserverMarshalingNerdbankMessagePackTests.cs	Removes conditional compilation and adds PolyType support
test/StreamJsonRpc.Tests/MarshalableProxyTests.cs	Updates test interfaces with TypeShape attributes and corrects typo
test/StreamJsonRpc.Tests/MarshalableProxyNerdbankMessagePackTests.cs	Removes conditional compilation flags
test/StreamJsonRpc.Tests/JsonRpcProxyGenerationTests.cs	Adds TypeShape attributes to test interfaces
test/StreamJsonRpc.Tests/DisposableProxyTests.cs	Removes conditional compilation for MessagePack tests
test/StreamJsonRpc.Tests/AsyncEnumerableTests.cs	Adds TypeShape attributes to test interfaces
test/StreamJsonRpc.Tests/ArchitectureTests.cs	Updates test to allow specific generated types
Multiple analyzer test files	Adds TypeShape attributes and updates test expectations
src/StreamJsonRpc/SystemTextJsonFormatter.cs	Updates marshaling to use RpcTargetMetadata
src/StreamJsonRpc/RpcMarshaledContext.cs	Refactors to non-generic base class
src/StreamJsonRpc/Reflection/ProxyBase.cs	Major refactor adding source-generated proxy support and type checking
src/StreamJsonRpc/Reflection/MessageFormatterRpcMarshaledContextTracker.cs	Updates marshaling logic for new proxy system

Comments suppressed due to low confidence (1)

test/StreamJsonRpc.Tests/JsonRpcProxyGenerationTests.cs:1

• The test method name 'Interface_HasAsyncDisposeWithoutIDisposable' is more descriptive than the previous name, correctly indicating it tests async dispose functionality.

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