RFR: 8349058: 'internal proprietary API' warnings make javac warnings unusable

[Liam Miller-Cushon]

This change is a partial backout of [JDK-8332744](https://bugs.openjdk.org/browse/JDK-8332744). The logic was reverted, but the test was preserved and updated to reflect the updated behaviour, and some cleanups to benchmark code were kept.

This restores the ability to use `-XDignore.symbol.file` as an ad-hoc suppression mechanism for `sunapi` diagnostics, see discussion in [JDK-8349058](https://bugs.openjdk.org/browse/JDK-8349058).

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Commit messages:
 - 8349058: 'internal proprietary API' warnings make javac warnings unusable

Changes: https://git.openjdk.org/jdk/pull/23448/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23448&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8349058
  Stats: 87 lines in 2 files changed: 30 ins; 38 del; 19 mod
  Patch: https://git.openjdk.org/jdk/pull/23448.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23448/head:pull/23448

PR: https://git.openjdk.org/jdk/pull/23448