[jdk11u-dev] RFR: 8249548: backward focus traversal gets stuck in button group

[Zhengyu Gu]

A clean backport for parity with Oracle 11.0.14.

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Commit messages:
 - Backport 22bb597d0d2d901c5c8227ea700ab27c670dd545

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/199/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=199&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8249548
  Stats: 1157 lines in 5 files changed: 538 ins; 618 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/199.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/199/head:pull/199

PR: https://git.openjdk.java.net/jdk11u-dev/pull/199