RFR: 8324680: Replace NULL with nullptr in JVMTI generated code

[Alex Menkov]

On Thu, 15 Feb 2024 08:46:43 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

> This enhancement replaces uses of NULL with nullptr in the XML-description files for JVMTI. These are the files `hotsport/share/prims/jvmti.xml` and `hotspot/share/prims/jvmti*.xls`.
> 
> The following files are auto-generated from the `jvmti.xml` and `*.xsl files` in the `build/<CFG>/variant-server/gensrc/jvmtifiles': `jvmti.h`, `jvmti.html`, `jvmtiEnter.cpp`, `jvmtiEnterTrace.cpp`, `jvmtiEnv.hpp`
> 
> This addresses a category of NULL uses that wasn't dealt with by:
>  [JDK-8299837](https://bugs.openjdk.org/browse/JDK-8299837).
>  
>  Testing:
>    - TBD: run mach5 tiers1-3

Marked as reviewed by amenkov (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/17866#pullrequestreview-1884223391