RFR: 8303755: Clean up around JavacElements.getAllMembers [v4]

[Pavel Rappo]

> Please review this cleanup which consists of commentary changes and code simplifications.

Pavel Rappo has updated the pull request incrementally with one additional commit since the last revision:

  Clarify an iterator comment

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12904/files
  - new: https://git.openjdk.org/jdk/pull/12904/files/140afc8a..cf908193

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12904&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12904&range=02-03

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/12904.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12904/head:pull/12904

PR: https://git.openjdk.org/jdk/pull/12904