fix: InvalidOperationException from RecipeService.Search()

[jonpryor]

Context: #1726
Context: #1728

Build and run Chefs.csproj for e.g. net10.0-desktop and NativeAOT while using Uno 6.6.0-dev.3:

sed -i '' 's/"Uno.Sdk": ".*"/"Uno.Sdk": "6.6.0-dev.3"/g' global.json
git clean -xdf Chefs{,.Api}
dotnet publish -c Release -r osx-x64 -f net10.0-desktop -p:TargetFrameworkOverride=net10.0-desktop \
  -bl Chefs/Chefs.csproj -p:UseSkiaRendering=true -p:SkiaPublishAot=true \
  -p:SkiaPublishAot=true \
  -p:IlcGenerateMapFile=true -p:IlcGenerateMstatFile=true -p:IlcGenerateDgmlFile=true -p:IlcGenerateMetadataLog=true \
  -p:EmitCompilerGeneratedFiles=true -p:CompilerGeneratedFilesOutputPath=`pwd`/_gen
Chefs/bin/Release/net10.0-desktop/osx-x64/publish/Chefs

From the launch screen:

1. Click Skip
2. Click  Sign in with Apple
3. Click 🔍Search on the left
4. In the Search box, type m

When doing this with e838af9, the search results screen shows:

An error occurred.

…which isn't particularly helpful.

If you do all this with #1728 applied, the Console log shows:

fail: Chefs.Business.Services.Recipes.RecipeService[0]
      Failed to search recipes with term m
      System.InvalidOperationException: Reflection-based serialization has been disabled for this application. Use the IServiceCollection.AddJsonTypeInfo() or IHostBuilder.UseSerialization(IHostBuilder, IEnumerable<IJsonTypeInfoResolver>, Action<IServiceCollection>) extension methods to enable JSON deserialization for type `System.Collections.Generic.Dictionary`2[[System.String, System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[Chefs.Business.Models.SearchHistory, Chefs, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]`.
         at Uno.Extensions.Serialization.SystemTextJsonSerializer.FromStream(Stream, Type) + 0x88
         at Uno.Extensions.Serialization.SerializerExtensions.FromStream[T](ISerializer, Stream) + 0x34
         at Uno.Extensions.Configuration.WritableOptions`1.<UpdateAsync>d__10.MoveNext() + 0x292
      --- End of stack trace from previous location ---
         at Chefs.Business.Services.Recipes.RecipeService.<SaveSearchHistory>d__51.MoveNext() + 0x5d
      --- End of stack trace from previous location ---
         at Chefs.Business.Services.Recipes.RecipeService.<SearchCore>d__24.MoveNext() + 0x8a
      --- End of stack trace from previous location ---
         at Chefs.Business.Services.Recipes.RecipeService.<Search>d__23.MoveNext() + 0x175

which shows what the problem is: RecipeService.Search() tries to save the search history, but JSON serialization does not support Dictionary<string, SearchHistory>, so an InvalidOperationException is thrown.

(Unfortunately the exception is basically swallowed; PR #1728 adds logging to that code path, and was needed to diagnose this issue.)

Update MockEndpointContext to emit JSON serialization metadata for Dictionary<string, SearchHistory>, so that Search now works.

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