RFR: 8342730: Get rid of SummaryDiff in VMATree

[Johan Sjölen]

On Wed, 13 Aug 2025 13:33:36 GMT, Afshin Zafari <azafari at openjdk.org> wrote:

> `SummaryDiff` result of any `register_mapping()` call, is passed into the function rather than returned. This enables avoiding copying the structure to/from the stack.
> 
> Tests:
> local linux-x64-debug: NMT gtests and JTREGs passed.

Thanks!

LGTM

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Marked as reviewed by jsjolen (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/26761#pullrequestreview-3135084602