Restore .NET 10 solution build

[xincheng213618]

What changed

• repair the malformed RenderEditorToCanvasLegacy method left by the recent Skia merge
• keep the selection rectangle calculation in RectangleF
• align WpfNodeEdittorDemo with the net10.0-windows library target
• suppress the new WFO1000 designer serialization diagnostic for the legacy WinForms controls

Why

The current main branch cannot restore or compile: the WPF demo targets .NET 8 while the library targets .NET 10, and STNodeEditor.cs contains merge residue that produces syntax errors. Once those are fixed, the .NET 10 WinForms analyzer reports WFO1000 as build errors for the legacy designer-facing properties.

Validation

• dotnet build .\WinNodeEditorTest.sln -c Debug --no-restore -v:q
• result: 0 errors, 266 existing warnings

This PR intentionally restores the existing WinForms/WPF-host baseline only. The native WPF implementation will be proposed separately so it does not obscure this repair.

[xincheng213618]

已将这组基线构建修复合并到 #40 的同一分支中，后续只保留 #40 作为统一的原生 WPF PR，避免维护者需要合并两次。