RFR: 8303882: Refactor some iterators in jdk.compiler

[Pavel Rappo]

Please review this refactoring to iterators in jdk.compiler. The refactoring delegates more to collections framework, while retaining the performance characteristics of bespoke iterators. The refactoring also adds inline comments, @Override annotations, and fixes some trivial bugs (as can be seen in the added test, which is slightly augment from that suggested by Jan Lahoda here https://github.com/openjdk/jdk/pull/12904#discussion_r1129777660).

I'll add a comment here once I have benchmarked the change formally.

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Commit messages:
 - Add a correctness test
 - Refactor the test
 - Add a test that the unfixed version fails
 - Change the test bug id and comment style
 - Add the test suggest by Jan Lahoda
 - Unify empty iterator in List and Iterators
 - Remove bespoke empty iterator in List
 - Initial commit from 8303755

Changes: https://git.openjdk.org/jdk/pull/12949/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12949&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303882
  Stats: 219 lines in 3 files changed: 179 ins; 33 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/12949.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12949/head:pull/12949

PR: https://git.openjdk.org/jdk/pull/12949