RFR: 8219014: (bf) Add absolute bulk put methods which accept a source Buffer

[Brian Burkhalter]

Please review this proposed fix. The previous incarnation of this review was most recently in mail threads [1, 2] under the old Hg SCM. The implementation changes proposed here are derived from the final (.02) patch posted in [1]. The corresponding CSR is [3].

The essence of the change is to move the bulk put buffer core functionality to a new method putBuffer(), modify the existing relative bulk put buffer method to call it, and add a new absolute bulk put buffer method which also calls it. The existing test for bulk put buffer functionality is modified to verify the new API.

This change builds on the work completed for JDK-5029431 (bulk put and get using an array) and JDK-8245121 (relative bulk put buffer with overlapping regions).

[1] http://mail.openjdk.java.net/pipermail/nio-dev/2020-June/007340.html
[2] http://mail.openjdk.java.net/pipermail/nio-dev/2020-July/007344.html
[3] https://bugs.openjdk.java.net/browse/JDK-8248431

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Commit messages:
 - 8219014: (bf) Add absolute bulk put methods which accept a source Buffer

Changes: https://git.openjdk.java.net/jdk/pull/969/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=969&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8219014
  Stats: 205 lines in 4 files changed: 186 ins; 15 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/969.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/969/head:pull/969

PR: https://git.openjdk.java.net/jdk/pull/969