RFR: 8233451: (fs) Files.newInputStream() cannot be used with character special files [v3]

[Brian Burkhalter]

> Add `isOther` and `available` methods to `FileChannelImpl` and the interfaces to native code and use these in `ChannelInputStream` to work around cases where a wrapped `FileChannelImpl` is not really seekable.

Brian Burkhalter has updated the pull request incrementally with two additional commits since the last revision:

 - 8233451: Do not initialize isOther to null
 - 8233451: Address reviewer comments; convert test to JUnit 5

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Changes:
  - all: https://git.openjdk.org/jdk/pull/21508/files
  - new: https://git.openjdk.org/jdk/pull/21508/files/51df5d81..492659f6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21508&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21508&range=01-02

  Stats: 62 lines in 4 files changed: 32 ins; 6 del; 24 mod
  Patch: https://git.openjdk.org/jdk/pull/21508.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21508/head:pull/21508

PR: https://git.openjdk.org/jdk/pull/21508