RFR: 8298478: (fs) Path.of should allow input to include long path prefix [v2]

[Brian Burkhalter]

> Remove the long path `\?` or `\?\UNC` prefix before creating the `WindowsPath` instance..

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

  8298478: Verify parsed type is acceptable for prefix type; add some cases to test

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12423/files
  - new: https://git.openjdk.org/jdk/pull/12423/files/34bb5b56..89d757f4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12423&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12423&range=00-01

  Stats: 59 lines in 2 files changed: 42 ins; 13 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/12423.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12423/head:pull/12423

PR: https://git.openjdk.org/jdk/pull/12423