Revert ImGui.NET dependency changes.

src/ImGui.NET/ImGui.NET.csproj

@@ -16,9 +16,9 @@
     <RootNamespace>ImGuiNET</RootNamespace>
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="System.Numerics.Vectors" Version="4.6.0-preview4.19164.7" />
+    <PackageReference Include="System.Numerics.Vectors" Version="4.4.0" />
-    <PackageReference Include="System.Runtime.CompilerServices.Unsafe" Version="5.0.0-rc.1.20451.14" />
+    <PackageReference Include="System.Runtime.CompilerServices.Unsafe" Version="4.4.0" />
-    <PackageReference Include="System.Buffers" Version="4.6.0-preview1-26912-03" />
+    <PackageReference Include="System.Buffers" Version="4.4.0" />
   </ItemGroup>
   <ItemGroup>
     <Content Include="..\..\deps\cimgui\win-x86\cimgui.dll">