[jdk21u-dev] RFR: 8324678: Replace NULL with nullptr in HotSpot gtests

[Goetz Lindenmaier]

test/hotspot/gtest/compiler/test_directivesParser.cpp
8327986: ASAN reports use-after-free in DirectivesParserTest.empty_object_vm
was already backported.
Failed chunk not applicable, skipped.

test/hotspot/gtest/gc/shared/test_bufferNodeAllocator.cpp
History of this file differs in a row of changes.
But here only Copyright needs to be resolved.

I backport this for parity with 21.0.8-oracle.

I don't really see why this was backported. But let's go 
along anyways, this is test-only coding and just a bit
tedious to prepare. But it might make later backports
much easier.

Resolved files in detail:

test/hotspot/gtest/jfr/test_adaptiveSampler.cpp
8313552: Fix -Wconversion warnings in JFR code
missing in 21.  This change sounds like a nice-to-have in 21,
but it is large.

test/hotspot/gtest/logging/test_logConfiguration.cpp
test/hotspot/gtest/logging/test_logTagSet.cpp
8299825: Move StdoutLog and StderrLog to LogConfiguration
missing in 21. Adapted all remaining NULLs.


test/hotspot/gtest/metaspace/test_binlist.cpp
8307356: Metaspace: simplify BinList handling
missing in 21. Not a candidate for backport.
One trivial resolve.


test/hotspot/gtest/metaspace/test_metaspacearena_stress.cpp
8307356: Metaspace: simplify BinList handling
8314654: Metaspace: move locking out of MetaspaceArena
missing in 21. Not candidates for backport.
Resolved and flipped one additional NULL.

test/hotspot/gtest/runtime/test_os_linux.cpp
8261894: Remove support for UseSHM
not in 21 and not a candidate, and later change
8341722: Fix some warnings as errors when building on Linux with toolchain clang
was already backported.
Resolved all remaining NULLs.

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

Commit messages:
 - Backport c1281e6b45ed167df69d29a6039d81854c145ae6

Changes: https://git.openjdk.org/jdk21u-dev/pull/1476/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1476&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324678
  Stats: 584 lines in 74 files changed: 0 ins; 0 del; 584 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1476.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1476/head:pull/1476

PR: https://git.openjdk.org/jdk21u-dev/pull/1476