[SE-0416] Put the key path literals subtyping proposal into review

Author: rjmccall

proposals/NNNN-keypath-function-subtyping.md renamed to proposals/0416-keypath-function-subtyping.md

@@ -1,9 +1,9 @@
 # Subtyping for keypath literals as functions
 
-* Proposal: [SE-NNNN](NNNN-keypath-function-subtyping.md)
+* Proposal: [SE-0416](0416-keypath-function-subtyping.md)
 * Authors: [Frederick Kellison-Linn](https://github.com/jumhyn)
 * Review Manager: [John McCall](https://github.com/rjmccall)
-* Status: **Awaiting review**
+* Status: **Active review (December 13, 2023...January 2, 2024)**
 * Implementation: [apple/swift#39612](https://github.com/apple/swift/pull/39612)
 * Review: ([pitch](https://forums.swift.org/t/pitch-generalize-keypath-to-function-conversions/52681))