RFR: 8280866: SuppressWarnings does not work properly in package-info and module-info

[Jan Lahoda]

`@SuppressWarnings` is not handled properly in `module-info` and, after https://bugs.openjdk.java.net/browse/JDK-8280744, also not in `package-info`. This patch attempts to fix that, by correctly deferring the warnings, and the printing them at an appropriate point.

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Commit messages:
 - Cleanup.
 - 8280866: SuppressWarnings does not work properly in package-info and module-info

Changes: https://git.openjdk.java.net/jdk/pull/7266/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7266&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280866
  Stats: 247 lines in 4 files changed: 234 ins; 0 del; 13 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7266.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7266/head:pull/7266

PR: https://git.openjdk.java.net/jdk/pull/7266