[jdk13u-dev] RFR: 8234687: change javap reporting on unknown attributes

[Ekaterina Vergizova]

I'd like to backport 8234687 to 13u for parity with 11u.
The patch applies cleanly.
Tested with tier1; new test fails without the patch, passes with it.

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Commit messages:
 - Backport 6025207be877a4081016371e52e9560f4e076552

Changes: https://git.openjdk.java.net/jdk13u-dev/pull/92/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk13u-dev&pr=92&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8234687
  Stats: 141 lines in 2 files changed: 136 ins; 3 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk13u-dev/pull/92.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk13u-dev pull/92/head:pull/92

PR: https://git.openjdk.java.net/jdk13u-dev/pull/92