RFR: Updated directory mapping for JDK 16

[Jesper Wilhelmsson]

A couple of new directories has been added in JDK 16.

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Commit messages:
 - Updated directory mapping for JDK 16

Changes: https://git.openjdk.java.net/guide/pull/54/files
 Webrev: https://webrevs.openjdk.java.net/?repo=guide&pr=54&range=00
  Stats: 5 lines in 1 file changed: 2 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/guide/pull/54.diff
  Fetch: git fetch https://git.openjdk.java.net/guide pull/54/head:pull/54

PR: https://git.openjdk.java.net/guide/pull/54