Migrate libcore benchmarks to BenchmarkRule

This is part of a larger migration effort to move all AndroidX
benchmarks to use BenchmarkRule instead of PerfStatusReporter. It's just the same boring change across all tests.
(cherry picked from https://android-review.googlesource.com/q/commit:2e93eddac8569049a18b11f3971269617563b243)

Merged-In: I309cb9a23102a9ae3680052fa92cd365dacd1443
Change-Id: I309cb9a23102a9ae3680052fa92cd365dacd1443