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

[azmy60]

Thanks for the PR! I think this could be simpler by avoiding the extra loop. For example:

const rowsNeedingHeightInit = [];
renderedRows.forEach((row) => {
    row.rendered();

    if(!row.heightInitialized) {
        row.calcHeight(true);
        rowsNeedingHeightInit.push(row);
    }
});

rowsNeedingHeightInit.forEach((row) => {
    row.setCellHeight();
});

[kunaljaykam]

thank you @azmy60 for the review. i agree but that would save one boolean check per row, but the performance win separating dom writes from dom reads will go away. rendered() triggers dom writes and calcHeight() reads layout properties combining them in one loop forces a browser reflow on every row. keeping them separate batches all writes first, then all reads, so the browser only reflows once.

[azmy60]

@kunaljaykam Ah I see. I wasn't aware of layout thrashing. Great catch!