RFR: 8178355: IdentityHashMap uses identity-based comparison for values everywhere except remove(K,V) and replace(K,V,V) [v6]

[liach]

> Explicitly implement `remove` and `replace` in `IdentityHashMap` to compare values by identity. Updated API documentation of these two methods ([Preview](https://cr.openjdk.java.net/~liach/8178355/IdentityHashMap.html#remove(java.lang.Object,java.lang.Object))) to mention such behavior.

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

  Spec updates and clarifications.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/8259/files
  - new: https://git.openjdk.org/jdk/pull/8259/files/fc2218f0..6874dc84

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=8259&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=8259&range=04-05

  Stats: 33 lines in 1 file changed: 18 ins; 0 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/8259.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/8259/head:pull/8259

PR: https://git.openjdk.org/jdk/pull/8259