RFR: 8335905: CompoundElement API cleanup [v2]

[Chen Liang]

> `CompoundElement` already inherits `Iterable` and its `forEach(Consumer)`, thus we can remove `Iterable elements()` and `forEachElements(Consumer)`.

Chen Liang has updated the pull request incrementally with one additional commit since the last revision:

  Two usages in tier3

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20103/files
  - new: https://git.openjdk.org/jdk/pull/20103/files/ea069e81..9caa520d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20103&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20103&range=00-01

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/20103.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20103/head:pull/20103

PR: https://git.openjdk.org/jdk/pull/20103