RFR: 8349812: (fs) Files.newByteChannel with empty path name and CREATE_NEW throws unexpected exception [v4]

[Maxim Kartashev]

> `UnixFileChannelFactory.open()` checks for the current directory by looking at the first byte of the name, which in case of an empty path is simply not there. This check throws an `ArrayIndexOutOfBoundsException` and prevents the correct exception from being thrown.
> 
> The suggested solution is to use another method that translates a path name into a byte array called `getByteArrayForSysCalls()` that is specifically designed to handle the case of empty path names.
> 
> Tested by running `java/nio` tests on Linux.

Maxim Kartashev has updated the pull request incrementally with one additional commit since the last revision:

  Fixed the test to pass on Windows also

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Changes:
  - all: https://git.openjdk.org/jdk/pull/23560/files
  - new: https://git.openjdk.org/jdk/pull/23560/files/c415adae..fe5c10b9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23560&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23560&range=02-03

  Stats: 5 lines in 1 file changed: 3 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/23560.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23560/head:pull/23560

PR: https://git.openjdk.org/jdk/pull/23560