[BUG] Java 15: DecimalFormatSymbols overrides equals but not hashCode

[Rob Spoor]

In Java 14 and before, DecimalFormatSymbols had overrides for both 
equals and hashCode. In Java 15, the override for hashCode has 
disappeared, and it now inherits hashCode from java.lang.Object. That 
means it now violates the contract for equals + hashCode: two equal 
DecimalFormatSymbols instances can have different hash codes.