RFR: 8320370: NMT: Change MallocMemorySnapshot to simplify code. [v3]

[Stefan Karlsson]

On Thu, 23 Nov 2023 11:12:23 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

>> Hi,
>> 
>> `MallocMemorySnapshot` used to be initialized in a quite non-standard way, using global placement new on an array of `size_t` of the size required to fit `MallocMemorySnapshot`. This looks like it was intended to circumvent some `ResourceObj` internals, but I'm unsure of its purpose. This change does what you expect a regular initialization of a global variable to look like.
>> 
>> ~Currently running through tier1.~ GHA passed and so did tier1 on Oracle CI.
>
> Johan Sjölen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove AnyObj inheritance

With this change it now seems unnecessary to keep the as_snapshot() functions. Right?

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PR Review: https://git.openjdk.org/jdk/pull/16724#pullrequestreview-1757896996