Promote `ServiceReference` to stable

[abstratt]

Fixes: #30858

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[abstratt]

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[abstratt]

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[abstratt]

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[abstratt]

Release notes (which links to the documentation that was updated):

https://builds.gradle.org/repository/download/Gradle_Master_Check_BuildDistributions/90469529:id/distributions/gradle-8.12-docs.zip!/gradle-8.12-20241018205650%2B0000/docs/release-notes.html#promoted-features

[abstratt]

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