RFR: 8303260: (fc) FileChannel::transferFrom should support position > size() [v3]

[Brian Burkhalter]

> Enhance `FileChannel::transferFrom` to extend the channel's file if `position > size()`. This is consistent with `FileChannel::write(ByteBuffer, long)`.

Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:

  8303260: Address reviewer comments on test

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12797/files
  - new: https://git.openjdk.org/jdk/pull/12797/files/0639c239..085746fa

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12797&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12797&range=01-02

  Stats: 23 lines in 1 file changed: 8 ins; 4 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/12797.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/12797/head:pull/12797

PR: https://git.openjdk.org/jdk/pull/12797