[statsd] Updated statsdstats containers according to usage patterns

- added benchmarks to justify unordered_map vs map benefits
- for high frequency dicts with number of keys > 500 unordered_map
  works better

Bug: 267849332
Test: statsd_benchmark
Change-Id: I0b62204399ce9e7c0096e10033a8d685b1a7c6d8
7 files changed