Preserve antiforgery token

[ilonatommy]

Fix antiforgery token trimming in Blazor WebAssembly prerendering

Add DynamicDependency attributes to prevent IL trimming of antiforgery type.

Description

When a Blazor WebAssembly app with Individual Identity authentication is published with PublishTrimmed=true, the antiforgery token persisted during SSR is not restored during the SSR-to-WASM handoff. This causes the <AntiforgeryToken> component to render nothing in interactive mode, breaking form submissions.

Root cause: The IL trimmer removes DefaultAntiforgeryStateProvider.CurrentToken property and AntiforgeryRequestToken constructor because they're only accessed via reflection by the persistent state system.

Fix: Add [DynamicDependency(JsonSerialized, typeof(...))] attributes on WebAssemblyHostBuilder.InitializeDefaultServices() to preserve:

• DefaultAntiforgeryStateProvider - ensures the [PersistentState] CurrentToken property is preserved
• AntiforgeryRequestToken - ensures the constructor and properties are preserved for JSON deserialization

Known workarounds:

<linker>
	<!--  AntiforgeryRequestToken deserialization issues  -->
	<assembly fullname="Microsoft.AspNetCore.Components.Web">
		<type fullname="Microsoft.AspNetCore.Components.Forms.AntiforgeryRequestToken" preserve="all"/>
	</assembly>
	<assembly fullname="Microsoft.AspNetCore.Components.WebAssembly">
		<type fullname="Microsoft.AspNetCore.Components.Forms.DefaultAntiforgeryStateProvider" preserve="all"/>
	</assembly>
</linker>

Fixes #64693

[Copilot]

Pull request overview

This PR fixes a critical trimming issue in Blazor WebAssembly applications with Individual Identity authentication. When published with PublishTrimmed=true, the antiforgery token state was being lost during the SSR-to-WASM handoff, causing form submissions to break. The fix adds DynamicDependency attributes to preserve the necessary types from IL trimming.

Key changes:

• Added [DynamicDependency(JsonSerialized, typeof(DefaultAntiforgeryStateProvider))] to preserve the CurrentToken property marked with [PersistentState]
• Added [DynamicDependency(JsonSerialized, typeof(AntiforgeryRequestToken))] to preserve the constructor and properties for JSON deserialization
• These attributes are placed on InitializeDefaultServices() method, following the established pattern used elsewhere in the codebase