RFR: 8286671: (fc) Modify sun.nio.ch.FileChannelImpl.map0() to accept a FileDescriptor parameter [v2]

[Brian Burkhalter]

> Add a `FileDescriptor` as the first parameter of `map0()` and remove from the corresponding native code the use of `fd_chan`.

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

  8286671: Rename initIDs() to allocationGranularity0()

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8689/files
  - new: https://git.openjdk.java.net/jdk/pull/8689/files/1b022d82..0c707e41

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8689&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8689&range=00-01

  Stats: 8 lines in 3 files changed: 0 ins; 1 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8689.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8689/head:pull/8689

PR: https://git.openjdk.java.net/jdk/pull/8689