[jdk13u-dev] RFR: 8249251: [dark_mode ubuntu 20.04] The selected menu is not highlighted in GTKLookAndFeel

[Yuri Nesterenko]

Tried with different WMs. The fix seems working well with SwingSet2; automatic swing tests don't show any regression.

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Commit messages:
 - Backport be2a92d8c7365c7aa79a43b53139e2f57fb15390

Changes: https://git.openjdk.java.net/jdk13u-dev/pull/119/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk13u-dev&pr=119&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8249251
  Stats: 303 lines in 2 files changed: 225 ins; 75 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk13u-dev/pull/119.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk13u-dev pull/119/head:pull/119

PR: https://git.openjdk.java.net/jdk13u-dev/pull/119