Please support ColumnVirtualization in a Grid that also has multi-column headers (column bands) and locked columns, all three at once.

Follows ticket 1720022, where Ivan Danchev confirmed two defects in this combination (Telerik UI for Blazor 15.1.0, Blazor Server, ScrollMode Virtual, 45 columns of fixed px width in bands, the first band locked, Grid Width in px):

1. A band's header colspan is computed from its visible leaf columns and ignores the columns hidden by virtualization, so the header row goes out of step with the data rows and a band partly in view shows no title.

2. With any locked column the virtualizer merges every hidden column into one spacer cell. The spacer is a whole number of columns wide, so it cannot match an arbitrary scroll offset and leaves an empty strip, narrower than one column, between the locked block and the first scrolled column, in the header and every row. The spacer also carries the first hidden column's band into the header row.

Why it matters: on Blazor Server every rendered cell is a component held on the circuit. For our 45-column logbook grid the cells and loading placeholders are most of each user's memory (about 50 MB of render tree), and column virtualization would cut that by about two thirds. Wide data grids are usually grouped into bands with an identifying block locked on the left, so the combination is the normal case for a grid wide enough to need column virtualization.

Related: feedback items 1546425 and 1538964.