Create a histogram from double values in a raster.
FastMapHistogram only works with integer values, which is good for performance
but means that, in order to use FastMapHistogram with double values, each value
must be multiplied by a power of ten to preserve significant fractional digits.
For example, if you want to save one significant digit (2.1 from 2.123), set
sigificantDigits to 1, and the histogram will save 2.1 as "21".
Important: Be sure that the maximum value in the rater multiplied by
10 ^ significantDigits does not overflow Int.MaxValue (2,147,483,647).