RFR: 8273261: Replace 'while' cycles with iterator with enhanced-for in java.base

[Andrey Turbanov]

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.

Similar cleanups:
* https://bugs.openjdk.java.net/browse/JDK-8258006
* https://bugs.openjdk.java.net/browse/JDK-8257912

-------------

Commit messages:
 - [PATCH] Replace while cycles with iterator with enhanced-for in java.base

Changes: https://git.openjdk.java.net/jdk/pull/5328/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5328&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273261
  Stats: 93 lines in 11 files changed: 1 ins; 50 del; 42 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5328.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5328/head:pull/5328

PR: https://git.openjdk.java.net/jdk/pull/5328