[jdk11u-dev] RFR: 8322239: [macos] a11y : java.lang.NullPointerException is thrown when focus is moved on the JTabbedPane

[Goetz Lindenmaier]

I backport this for parity with 11.0.24-oracle.

I resolved Copyright and import (actually unneeded) in JTabbedPane.java.

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Commit messages:
 - Backport 3b1062d45df69d4cf8479c6a65602bd2453ab885

Changes: https://git.openjdk.org/jdk11u-dev/pull/2601/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2601&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322239
  Stats: 115 lines in 2 files changed: 111 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2601.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2601/head:pull/2601

PR: https://git.openjdk.org/jdk11u-dev/pull/2601