fix(vtable): expose auto row real height

[fangsmile]

Summary

• Fix [Bug] autoHeight模式下设置defaultRowHeight不生效，通过setRowHeight也修改不了，customComputeRowHeight（）拿到的行高值一直为40 #5117
• Add realHeight to customComputeRowHeight so callbacks can read the computed auto row height
• Treat numeric defaultRowHeight as the minimum row height under autoHeight
• Add debug demo issue-5117-auto-height-real-height

Verification

• packages/vtable-editors: rushx build
• packages/vtable: rushx compile
• Chrome DevTools MCP: window.issue5117Check() => pass=true, realHeight=64, rowHeight=64