Advance RFC #0848 `"Deprecate array prototype extensions"` to Stage Ready for Release #1184

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Frontmatter stage must be 'accepted' before merging	0s
RFC must be in only one stage before merging (labels)	0s
Stage must be 'Exploring' (via label) for new RFC before merging	0s
Verify Accepted PR URL is correct	0s
Filename matches RFC number	0s
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