Entire row/column mouse selection in QTableView no longer works in Qt6

Steps to reproduce:

• Open a table view with row/column headers visible;
• Click on column (row) header section - entire column/row gets selected. Don't release the mouse button;
• Move the mouse to select other header sections.
• In Qt5 the selection was extended and all hovered columns/rows were selected;
• In Qt6 only one section is selected (the one under mouse cursor).

This bug is a result of QTBUG-92561 fix.

In QTableViewPrivate::selectColumn() the variable, now used to determine the start of the selection, ("currentSelectionStartIndex"), gets reset within

"selectionModel->setCurrentIndex(index, QItemSelectionModel::NoUpdate);"

call and points to just hovered section instead of original selection start.