RFR: 8291023: FileOutputStream.close() re-entrantly invokes itself after getChannel().force()

[Archie L. Cobbs]

IO stream classes like `FileOutputStream` can have assocated NIO channels.

When `close()` is invoked on one of these classes, it in turn invokes `close()` on the associated channel (if any). But when the associated channel's `close()` method is invoked, it in turn invokes `close()` on the associated stream (if any).

As a result, these IO stream `close()` methods invoke themselves reentrantly when there is an associated channel.

This is not a problem for these classes because they are written to handle this (i.e., they are idempotent), but it can be surprising (or worse, just silently bug-inducing) for subclasses that override `close()`.

There are two possible ways to address this:
1. Modify the code to detect and avoid the (unnecessary) reentrant invocations
2. Add a `@implNote` to the Javadoc so subclass implementers are made aware

This patch takes the second, more conservative approach.

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Commit messages:
 - Add @implNote's regarding close() invoking itself reentrantly.

Changes: https://git.openjdk.org/jdk/pull/13379/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13379&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8291023
  Stats: 15 lines in 3 files changed: 15 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13379.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13379/head:pull/13379

PR: https://git.openjdk.org/jdk/pull/13379