RFR: 8322256: Define and document GZIPInputStream concatenated stream semantics

[Archie Cobbs]

`GZIPInputStream` supports reading data from multiple concatenated GZIP data streams since [JDK-4691425](https://bugs.openjdk.org/browse/JDK-4691425). In order to do this, after a GZIP trailer frame is read, it attempts to read a GZIP header frame and, if successful, proceeds onward to decompress the new stream. If the attempt to decode a GZIP header frame fails, or happens to trigger an `IOException`, it just ignores the trailing garbage and/or the `IOException` and returns EOF.

There are several issues with this:

1. The behaviors of (a) supporting concatenated streams and (b) ignoring trailing garbage are not documented, much less precisely specified.
2. Ignoring trailing garbage is dubious because it could easily hide errors or other data corruption that an application would rather be notified about. Moreover, the API claims that a `ZipException` will be thrown when corrupt data is read, but obviously that doesn't happen in the trailing garbage scenario (so N concatenated streams where the last one has a corrupted header frame is indistinguishable from N-1 valid streams).
3. There's no way to create a `GZIPInputStream` that does _not_ support stream concatenation.

On the other hand, `GZIPInputStream` is an old class with lots of existing usage, so it's important to preserve the existing behavior, warts and all (note: my the definition of "existing behavior" here includes the bug fix in [JDK-7036144](https://bugs.openjdk.org/browse/JDK-7036144)).

So this patch adds a new constructor that takes two new parameters `allowConcatenation` and `allowTrailingGarbage`. The legacy behavior is enabled by setting both to true; otherwise, they do what they sound like. In particular, when `allowTrailingGarbage` is false, then the underlying input must contain exactly one (if `allowConcatenation` is false) or exactly N (if `allowConcatenation` is true) concatenated GZIP data streams, otherwise an exception is guaranteed.

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Commit messages:
 - Javadoc wording tweaks.
 - Merge branch 'master' into JDK-8322256
 - Clarify exceptions: sometimes ZipException, sometimes EOFException.
 - Merge branch 'master' into JDK-8322256
 - Javadoc wording tweaks.
 - Add "allowConcatenation" and "allowTrailingGarbage" to GZIPInputStream.

Changes: https://git.openjdk.org/jdk/pull/18385/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18385&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322256
  Stats: 303 lines in 2 files changed: 286 ins; 2 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/18385.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18385/head:pull/18385

PR: https://git.openjdk.org/jdk/pull/18385