Allows adjacent cells to be merged in layout manual table items.
From the table editor, select multiple cells in a rectangular
shape and then from the Table menu, click "Merge Selected Cells".
Merged cells can be un-merged via the "Split Selected Cells"
menu action.
Fixes#51694
The original workaround was only supposed to apply to QList/
QVector of QVariantMaps. By replacing them all in sip we
break mapping of signals defined in c++ which are emitted
by Python code.
Fixes exceptions after running processing algorithms in Qt6
builds.
