RFR: JDK-8344368 : IndependenceSwingTest.java and IndependenceAWTTest.java failed: Selected text & clipboard contents differs

[Harshitha Onkar]

The following two tests failed intermittently due to stability issues after JEP486 (Removal of Security Manager). Tests have been updated for stability. 
This test is applicable for linux platform only, hence `@requires (os.family == "linux")`  jtreg tag is added and the redundant OS check within the test is removed.

- java/awt/datatransfer/Independence/IndependenceAWTTest.java
- java/awt/datatransfer/Independence/IndependenceSwingTest.java

Multiple runs of the test on CI looks good and the tests pass.

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Commit messages:
 - removed author tags, delay changes
 - added missing import
 - datatransfer test changes

Changes: https://git.openjdk.org/jdk/pull/22490/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22490&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344368
  Stats: 166 lines in 2 files changed: 63 ins; 31 del; 72 mod
  Patch: https://git.openjdk.org/jdk/pull/22490.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22490/head:pull/22490

PR: https://git.openjdk.org/jdk/pull/22490