int getHeight(int row) {
			return heightsByRow.computeIfAbsent(row, k -> 0);
		}
A class to track all row heights for a given {@link MultiRowLayout}.   Multiple instances
of this class can be merged to create a total collection of row heights for more than one
{@link MultiRowLayout}, such as is done for the diff tool.  The merged row heights 
represent the total number of rows possible as well as the maximum possible height for a 
given row.
Ghidra/Framework/Docking/src/main/java/docking/widgets/fieldpanel/support/MultiRowLayout.java