RFR: 8267893: Improve EFH do get native/mixed stack traces for cores and live processes

[Leonid Mesnik]

EFH is improved to process cores and get mixed stack traces with jhsdb and native stack traces with gdb/lldb. It might be useful because hs_err doesn't contain info about all threads, sometimes it is even not generated.

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Commit messages:
 - Merge branch 'master' of https://github.com/openjdk/jdk into efh
 - EFH improvements

Changes: https://git.openjdk.java.net/jdk/pull/4234/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4234&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267893
  Stats: 188 lines in 13 files changed: 158 ins; 6 del; 24 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4234.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4234/head:pull/4234

PR: https://git.openjdk.java.net/jdk/pull/4234