RFR: 8305490: CommandProcessor command "dumpclass" produces classes with invalid field descriptors

[Adam Sotona]

CommandProcessor command "dumpclass" produces classes with invalid field descriptors. 

Proposed patch fixes `sun.jvm.hotspot.oops.InstanceKlass::getFieldSignatureIndex` to return correct `getSignatureIndex` instead of invalid `getGenericSignatureIndex`.

Added condition to  `ClhsdbDumpclass` test assures no errors are reported by `javap` in the dumped classes.

Please review.

Thank you,
Adam

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Commit messages:
 - added test condition
 - 8305490: CommandProcessor command "dumpclass" produces classes with invalid field descriptors

Changes: https://git.openjdk.org/jdk/pull/13321/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13321&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305490
  Stats: 2 lines in 2 files changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13321.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13321/head:pull/13321

PR: https://git.openjdk.org/jdk/pull/13321