[release/10.0] [DAC] fix dac_gc_heap marshalling

[github-actions]

Backport of #119393 to release/10.0

/cc @max-charlamb

Customer Impact

• Customer reported
• Found internally

Found while working on #119324. Since the GetGCInterestingInfoData DAC API marshalled the dac_gc_heap incorrectly, the SOS command !dumpgcdata gives incorrect results on server builds.

Regression

• Yes
• No

Unclear if this ever worked, or if other logic changed causing this to fail at some point.

Testing

Verfied by new test in the diagnostic repo.
See new test: dotnet/diagnostics#5562
See successful run with new test: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1140803&view=results

Risk

Low. This change does not modify the runtime; it only modifies the DAC build.

IMPORTANT: If this backport is for a servicing release, please verify that:

• The PR target branch is release/X.0-staging, not release/X.0.

Package authoring no longer needed in .NET 9

IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.

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[JulieLeeMSFT]

LGTM. Please check the pipeline results.