Given a raster and a raster representing it's zones, sets all pixels
within each zone to the percentage of those pixels having values equal
to that of the given pixel.
Percentages are integer values from 0 - 100.
ZonalPercentage does not currently support Double raster data.
If you use a Raster with a Double CellType (FloatConstantNoDataCellType, DoubleConstantNoDataCellType)
the data values will be rounded to integers.