RFR: 8290812: Add a test for ResourceHashtable [v5]

[Coleen Phillimore]

> I added a test for ResourceHashtable to show the interactions with it and Symbol* refcounting.
> Tested with tier1 on Oracle platforms.

Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:

  Use swap and copy value parameter trick for assignment operator.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9603/files
  - new: https://git.openjdk.org/jdk/pull/9603/files/caf3ba18..b3953376

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9603&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9603&range=03-04

  Stats: 11 lines in 1 file changed: 5 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/9603.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9603/head:pull/9603

PR: https://git.openjdk.org/jdk/pull/9603