RFR: 8244670: convert clhsdb "whatis" command from javascript to java

[Chris Plummer]

"whatis" is one of the old clhsdb commands that was written in javascript and lost when Nashorn support was removed. The old "whatis" is the same as the old "findpc", but also called LoadObject.lookup() on the address and also tried to determine the C++ Type of the address. However, with the improvements made to PointerFinder by JDK-8247514, findpc now also includes support for this (plus other types of address lookups), so these two commands will do the same thing. I'm still adding "whatis" since some people might still rely on it from when it worked in JDK 8, and may not know that findpc will do the same.

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Commit messages:
 - Add clhsdb whatis command

Changes: https://git.openjdk.java.net/jdk/pull/6887/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6887&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8244670
  Stats: 21 lines in 2 files changed: 21 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6887.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6887/head:pull/6887

PR: https://git.openjdk.java.net/jdk/pull/6887