Replaces while cycles with iterator with enhanced for in java.desktop

The patch was proposed by the Andrey Turbanov(turbanoff):
https://github.com/openjdk/jdk/pull/1574

There are few places in code where manual while loop is used with Iterator to iterate over Collection.
Instead of manual while cycles it's preferred to use enhanced-for cycle instead: it's less verbose, makes code easier to read and it's less error-prone.
It doesn't have any performance impact: java compiler generates similar code when compiling enhanced-for cycle.

See similar cleanup in C++ code - https://github.com/openjdk/jdk/pull/1707