Add benchmark-darwin and benchmark-darwin-core to collection playground
Add benchmark-darwin and benchmark-darwin-core to collection playground

benchmark:benchmark-darwin / -core isn't currently configured to produce
snapshots for androidx.dev so we cannot use projectOrArtifact. For now, just
include it as part of collection-playground so it can be used for collection's
iOS benchmarks.

Test: cd collection && ./gradlew bOS
Change-Id: I26df069ed3fba0d881792ce8e058c762d3652bf3

androidx/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx