RFR: 8292170: Convert CodeRootSetTable to use ResourceHashtable [v4]

[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?

Leo Korinth has updated the pull request incrementally with one additional commit since the last revision:

  can not use contains in combination with add without a lock

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11675/files
  - new: https://git.openjdk.org/jdk/pull/11675/files/0887a73e..32976d38

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11675&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11675&range=02-03

  Stats: 5 lines in 1 file changed: 0 ins; 2 del; 3 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