<Swing Dev> RFR: 8255916: [macos] javax/swing/JInternalFrame/6647340/bug6647340.java timed out

[Prasanta Sadhukhan]

This test has failed in one of jdk nightly testing although it always passed locally. Made the test use robot delays, waitForIdle() to make it more stable and appropriate to run in slower mach5 systems and also remove the dependancy on ExtendedRobot.
Mach5 job has been run for several iterations in all platforms. Link in JBS.

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Commit messages:
 - Initial fix

Changes: https://git.openjdk.java.net/jdk/pull/1115/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1115&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255916
  Stats: 65 lines in 1 file changed: 12 ins; 23 del; 30 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1115.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1115/head:pull/1115

PR: https://git.openjdk.java.net/jdk/pull/1115