RFR: 8287171: Refactor null caller tests to a single directory

[Tim Prinzing]

Created a test at test/jdk/jdk/nullCaller called NullCallerTest that creates a test module with some resources in it for the actual tests that occur at the native level. The native part was switched to c++ instead of c to make it easier to create helper objects that reduce the redundant code performing error checking. The two helper classes InstanceCall and StaticCall were placed in an include file called CallHelper.hpp. The main part of the tests are in exeNullCallerTest.cpp, and there is a separate function for each of the bug reports.

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Commit messages:
 - 8287171: Refactor null caller tests to a single directory

Changes: https://git.openjdk.java.net/jdk/pull/8934/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8934&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287171
  Stats: 1293 lines in 18 files changed: 511 ins; 780 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8934.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8934/head:pull/8934

PR: https://git.openjdk.java.net/jdk/pull/8934