[jdk8u-ri] RFR: 8071507: (ref) Clear phantom reference as soft and weak references do [v2]

[Poonam Bajaj]

> These changes backport the following fixes to jdk8u-ri:
> - 8071507: (ref) Clear phantom reference as soft and weak references do
> - 8143847: Remove REF_CLEANER reference category
> 
> With these changes, phantom references are automatically cleared by the garbage collector as soft and weak references.

Poonam Bajaj has updated the pull request incrementally with one additional commit since the last revision:

  Corrected documentation in package.html

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Changes:
  - all: https://git.openjdk.java.net/jdk8u-ri/pull/4/files
  - new: https://git.openjdk.java.net/jdk8u-ri/pull/4/files/8bee95e2..35aa32d0

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk8u-ri&pr=4&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk8u-ri&pr=4&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk8u-ri/pull/4.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk8u-ri pull/4/head:pull/4

PR: https://git.openjdk.java.net/jdk8u-ri/pull/4