RFR: 8292170: Convert CodeRootSetTable to use ResourceHashtable

[Leo Korinth]

I am replacing the old hash table with ResourceHashtable. In the process I am also removing the redundant `_length` field. By removing the `_length` field, a lot of asserts can be removed as the length will trivially match the length of the underlying table.

I would like to have feedback on the addition of `unlink_destruct(Function&& should_remove)`. I added it because I prefer to use a functor object that can be used by lambdas instead of an iterator object. However, I did add code to "destruct" resource objects when they are removed instead of just letting them be to reflect that we use `delete` on c-heap objects. Maybe I should remove this "improvement" and then maybe implement the function by calling the existing unlink?

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Commit messages:
 - 8292170: Convert CodeRootSetTable to use ResourceHashtable

Changes: https://git.openjdk.org/jdk/pull/11675/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11675&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292170
  Stats: 146 lines in 5 files changed: 38 ins; 83 del; 25 mod
  Patch: https://git.openjdk.org/jdk/pull/11675.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11675/head:pull/11675

PR: https://git.openjdk.org/jdk/pull/11675