[WIP] ref(native): port attachments to value-based API

[jpnurmi]

See:

• [0.17] ref!: sentry_value-based attachments sentry-native#1974

[github-actions]

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## Unreleased

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- port attachments to value-based API ([#1540](https://github.com/getsentry/sentry-unreal/pull/1540))

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