RFR: 8306320: BufferedImage spec needs clarification w.r.t its implementation of the WritableRenderedImage interface [v3]

[Martin Desruisseaux]

> `BufferedImage` implements the `WritableRenderedImage` interface. But the Javadoc is copied from `WritableRenderedImage`, while `BufferedImage` does something quite different. In particular, `TileObserver` are ignored. This pull request add `@implSlec` for explaining the default behaviour.
> 
> This commit has one specification change in `isTileWritable`: the exception type is changed from `ArrayIndexOutOfBoundsException` to `IllegalArgumentException` for matching the implementation. The logical conditions is also corrected.
> 
> This commit contains a trivial code change: `new Point(0,0)` is replaced by `new Point()` for saving a few byte codes.

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

  Replace "The default implementation" text by "This method".
  Other edits as commented on GitHub issue.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13506/files
  - new: https://git.openjdk.org/jdk/pull/13506/files/0f339543..217c6c0a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13506&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13506&range=01-02

  Stats: 14 lines in 1 file changed: 4 ins; 1 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/13506.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13506/head:pull/13506

PR: https://git.openjdk.org/jdk/pull/13506