[lworld] RFR: 8346307: [lworld] Document WeakHashMap and other apis that may throw IdentityException [v2]

[Roger Riggs]

> Add APINote  and javadoc for IdentityException where it will be useful to know that identity or value objects are treated differently. 
> Simplified WeakHashMap javadoc updates for IdentityException. 
> Added note to System.identityHashCode to include value objects.
> Added to class javadoc for IdentityHashMap for value objects.

Roger Riggs has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'openjdk:lworld' into 8346307-throws-identityexception
 - 8346307: [lworld] Document WeakHashMap and other apis that may throw IdentityException
   Add APINote  and javadoc for IdentityException where it will be useful to know.
   Simplified WeakHashMap javadoc updates for IdentityException.
   Added note to System.identityHashCode to include value objects.

-------------

Changes:
  - all: https://git.openjdk.org/valhalla/pull/1327/files
  - new: https://git.openjdk.org/valhalla/pull/1327/files/339bc421..2aae8e67

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1327&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1327&range=00-01

  Stats: 490 lines in 41 files changed: 308 ins; 6 del; 176 mod
  Patch: https://git.openjdk.org/valhalla/pull/1327.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1327/head:pull/1327

PR: https://git.openjdk.org/valhalla/pull/1327