RFR: 8371953: Document null handling in core reflection APIs [v6]

[Chen Liang]

> A lot of core reflection APIs are from antique times, which have their own null handling behavior. Such behaviors are often not documented in the specification; we should document rejected null arguments and accepted null arguments (including array elements) explicitly.
> 
> In the investigation, I found `Class.isNestmateOf` (inconsistent) and `AnnotatedType`'s implementation of `AnnotatedElement` methods (required by specification) are missing null checks. I consider these unlikely to be a user dependency and added new null checks.

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

  Redundant extra sentences

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Changes:
  - all: https://git.openjdk.org/jdk/pull/28336/files
  - new: https://git.openjdk.org/jdk/pull/28336/files/757ffefd..975f98d8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28336&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28336&range=04-05

  Stats: 4 lines in 1 file changed: 0 ins; 3 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/28336.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28336/head:pull/28336

PR: https://git.openjdk.org/jdk/pull/28336