RefSource generator generates setter instead of init

[ManickaP]

• This issue is blocking
• This issue is causing unreasonable pain

Generated Ref source from System.Net.Quic src for the new API in dotnet/runtime#101534 (using dotnet msbuild /t:GenerateReferenceAssemblySource).
Source:

public readonly struct QuicStreamCapacityChangedArgs
{
    public int BidirectionalIncrement { get; init; }
    public int UnidirectionalIncrement { get; init; }
}

Generated Ref:

public readonly partial struct QuicStreamCapacityChangedArgs
{
    private readonly int _dummyPrimitive;
    public int BidirectionalIncrement { get { throw null; } set { } }
    public int UnidirectionalIncrement { get { throw null; } set { } }
}

Expected Ref:

public readonly partial struct QuicStreamCapacityChangedArgs
{
    public int BidirectionalIncrement { get { throw null; } init { } }
    public int UnidirectionalIncrement { get { throw null; } init { } }
}