RFR: 8287134: HttpURLConnection chunked streaming mode doesn't enforce specified size

[Conor Cleary]

### **Description**
When using `HttpURLConnection::setChunkedStreamingMode()`, the current documentation does not make it clear that the `chunklen` parameter refers to the amount of bytes sent on the wire per HTTP/1.1 chunk and _not_ the  payload length per chunk. The `chunklen` parameter takes into account the bytes used for the chunk size header, two CRLF characters and the possible payload length inclusively.

### **Summary of Changes & Justification**
The API text has been updated to reflect the actual behavior of the method as described above to avoid a similar bug being submitted in the future and to make it clear what the `chunklen` parameter specifies.

This change will require a csr.

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Commit messages:
 - 8287134: HttpURLConnection chunked streaming mode doesn't enforce specified size

Changes: https://git.openjdk.org/jdk/pull/12137/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12137&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8287134
  Stats: 5 lines in 1 file changed: 2 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/12137.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12137/head:pull/12137

PR: https://git.openjdk.org/jdk/pull/12137