RFR: 8290499: new File(parent, \"/\") breaks normalization – creates File with slash at the end

[Brian Burkhalter]

In `java.io.File`, change the constructors `File(File,String)` and `File(String,String)` so that they do not for typical cases return a `File` whose path has a trailing name separator.

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Commit messages:
 - 8290499: new File(parent, \"/\") breaks normalization – creates File with slash at the end

Changes: https://git.openjdk.org/jdk/pull/14109/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14109&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8290499
  Stats: 34 lines in 3 files changed: 28 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/14109.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14109/head:pull/14109

PR: https://git.openjdk.org/jdk/pull/14109