RFR: 8246739: InputStream.skipNBytes could be implemented more efficiently

[Brian Burkhalter]

Please review this modification of `java.io.InputStream.skipNBytes(long)` to improve its performance when `skip(long)` skips fewer than the requested number of bytes. In the current implementation, `skip(long)` is invoked once and, if not enough bytes have been skipped, then `read()` is invoked for each of the remaining bytes to be skipped. The proposed implementation instead repeatedly invokes `skip(long)` until the requested number of bytes has been skipped, or an error condition is encountered. For cases where `skip(long)` skips fewer bytes than the number requested, the new version was measured to be up to more than one thousand times faster than the old version. When `skip(long)` actually skips the requested number of bytes, the performance difference is insignificant.

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Commit messages:
 - 8246739: InputStream.skipNBytes could be implemented more efficiently

Changes: https://git.openjdk.java.net/jdk/pull/1329/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1329&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8246739
  Stats: 11 lines in 1 file changed: 2 ins; 3 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1329.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1329/head:pull/1329

PR: https://git.openjdk.java.net/jdk/pull/1329