En masse conversion from NULL to nullptr

[Johan Sjölén]

Hi Hotspot devs,

For the beginning of 2023 us at Oracle want to make a push to convert 
NULL into nullptr. This is something that has been in the works for some 
time, where conversions have been made as part of other PRs in a "change 
as you go" approach. This is taking a long time and there are tensions 
between local consistency and not cluttering reviews with cleanup 
changes. We'd therefore like to finish the job, so instead we
will be creating PRs which solely do this conversion. David Holmes has 
created a task for this (JDK-8299837) and subtasks are added for each
subdirectory. Therefore one subdirectory will be converted in a single 
PR. This will keep PR sizes down and split the reviewing up. I will be 
the one creating the subtasks and PRs.

After these changes you might have "legitimate" merge conflicts mixed in 
with NULL/nullptr conflicts if you merge directly to HEAD. In order to 
deal with the legitimate conflicts first, I suggest that you:

1. Merge on top of the commit just before the NULL/nullptr conversion 
that causes issues.
2. Merge on top of the NULL/nullptr conversion commit
3. Merge the rest of the way to HEAD


Best regards,
Johan Sjölén