RFR: 8220816: (fs) Files.createDirectory should make it more obvious that it fails when the directory already exists [v4]

[Brian Burkhalter]

> Slightly changes the specification of `Files.createDirectory` to highlight that it fails if a filesystem entity already exists at the given location.

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

  8220816: Improve consistency per review comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/28378/files
  - new: https://git.openjdk.org/jdk/pull/28378/files/3af34903..5c62cd5f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28378&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28378&range=02-03

  Stats: 17 lines in 1 file changed: 3 ins; 1 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/28378.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28378/head:pull/28378

PR: https://git.openjdk.org/jdk/pull/28378