RFR: 8312136: Modify runtime/ErrorHandling/TestDwarf.java to split dwarf and decoder testing

[David Holmes]

This change updates the test so that there are two variants: one expects to get good decoder parsing of the log lines, and one which doesn't. The decoder expecting variant is then ProblemListed.

The exception message in the failing decoder test case is modified to report the actual problem - see example output in JBS issue.

Tested locally and in GHA to get the failing linux-x86 case.

Thanks.

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Commit messages:
 - ProblemList the decoder checking test variant
 - 8312136: Modify runtime/ErrorHandling/TestDwarf.java to split dwarf and decoder testing

Changes: https://git.openjdk.org/jdk/pull/15895/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15895&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8312136
  Stats: 37 lines in 2 files changed: 30 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/15895.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15895/head:pull/15895

PR: https://git.openjdk.org/jdk/pull/15895