Update to MongoDB Driver 3.4.0

[nscheibe]

This pull request includes several updates to dependencies, a migration to .NET 8.0, and refactoring of MongoDB-related serializers. The most significant changes involve upgrading package versions, removing support for .NET 6.0, and improving the structure and functionality of the TypeObjectSerializer class.

Dependency Updates:

• Updated multiple package versions in Directory.Packages.props, including Moq (4.16.1 → 4.20.72), Snapshooter.Xunit (0.13.0 → 0.14.1), and Microsoft.SourceLink.GitHub (1.1.1 → 8.0.0), among others.
• Updated Microsoft.VisualStudio.Azure.Containers.Tools.Targets (1.17.0 → 1.21.0) and NSwag.AspNetCore (14.0.8 → 14.3.0) in samples/Directory.Packages.props.

Migration to .NET 8.0:

• Changed the target framework for multiple projects, including Migration.csproj and Migration.Tests.csproj, to net8.0 and removed support for net6.0. [1] [2] [3] [4]
• Removed IsExternalInit.cs conditionally included for net6.0 in Context.Tests.csproj.

MongoDB Serializer Refactoring:

• Refactored TypeObjectSerializer to expose an ObjectSerializer property, replacing the private _objectSerializer field. Updated methods to use this property for serialization and equality checks. [1] [2]
• Modified TryRegisterObjectSerializer in MongoDatabaseBuilder to register the ObjectSerializer from TypeObjectSerializer.
• Updated tests in MongoDatabaseBuilderTests.cs to assert against ObjectSerializer instead of TypeObjectSerializer. [1] [2] [3]

Codebase Simplification:

• Introduced System.Collections.Immutable to convert convention names to immutable lists in RegisterConventions for better immutability and safety.
• Removed unused using directives in MongoDatabaseBuilderTests.cs.

These changes improve compatibility with .NET 8.0, enhance dependency management, and refine the MongoDB serialization mechanism for better maintainability and performance.

[nscheibe]

All looks right

[bejto]

appruft