fix(rendering): optimize row height initialization in VirtualDomVertical

[kunaljaykam]

1. Fixes a gap from PR feat: renderer performance improvements #4134: Separates rendered() callbacks from height calculations
2. Follows existing patterns: Matches the _quickNormalizeRowHeight() approach (lines
   632-640)
3. Has precedent: Similar fix was already done for horizontal rendering (commit beff450)
4. Clear performance benefit: Reduces layout thrashing during initial render