RFR: 8326090: Rename jvmti_aod.h

[Kim Barrett]

Please review this trivial change that renames the file
test/hotspot/jtreg/vmTestbase/nsk/share/jvmti/aod/jvmti_aod.h to jvmti_aod.hpp,
and replace uses of NULL in the file.

The #include updates were performed mechanically, and build would fail if
there were mistakes. All of the including files have already had their
copyrights updated recently, as part of JDK-8324681. So the only interesting
(for some minimal value of "interesting") changes are in the renamed file.

Testing: mach5 tier1

-------------

Commit messages:
 - rename NULLs in jvmti_aod.hpp
 - rename jvmti_aod.h

Changes: https://git.openjdk.org/jdk/pull/17895/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17895&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8326090
  Stats: 33 lines in 27 files changed: 0 ins; 0 del; 33 mod
  Patch: https://git.openjdk.org/jdk/pull/17895.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17895/head:pull/17895

PR: https://git.openjdk.org/jdk/pull/17895