RFR: 8291970: Add TableStatistics get function to ResourceHashtable

[Coleen Phillimore]

Add a statistics_calculate function to ResourceHashtable so that we can use it for printing.  Also add a test.
Tested with tier1 on Oracle platforms (with and without product build).

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Commit messages:
 - 8291970: Add TableStatistics get function to ResourceHashtable

Changes: https://git.openjdk.org/jdk/pull/9775/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9775&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8291970
  Stats: 74 lines in 4 files changed: 71 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/9775.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9775/head:pull/9775

PR: https://git.openjdk.org/jdk/pull/9775