Potential Perf Gain: Use `LibraryImport` instead of `DllImport` when using .NET 7

[Niklas Mollenhauer]

When using .NET 7, there is a new attribute that can be used to mark p/invokes:
https://learn.microsoft.com/en-us/dotnet/standard/native-interop/pinvoke-source-generation

The API is kinda similar:

[DllImport(
    "nativelib",
    EntryPoint = "to_lower",
    CharSet = CharSet.Unicode)]
internal static extern string ToLower(string str);

becomes

[LibraryImport(
    "nativelib",
    EntryPoint = "to_lower",
    StringMarshalling = StringMarshalling.Utf16)]
internal static partial string ToLower(string str);

The key difference is that the code used to marshal the parameters is emitted during compile-time instead of run-time. This is faster but also opens the ability to do native AOT compilations.

I think d2dlib uses .NET 6, so this might not be relevant yet. But it might be for the next major LTS version.