RFR: 8327751: Convert javax/swing/JInternalFrame/6726866/bug6726866.java applet test to main

[Prasanta Sadhukhan]

Conversion of manual applet test to main based using PassFailJFrame manual framework

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Commit messages:
 - 8327751: Convert javax/swing/JInternalFrame/6726866/bug6726866.java applet test to main

Changes: https://git.openjdk.org/jdk/pull/18186/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18186&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327751
  Stats: 70 lines in 2 files changed: 18 ins; 30 del; 22 mod
  Patch: https://git.openjdk.org/jdk/pull/18186.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18186/head:pull/18186

PR: https://git.openjdk.org/jdk/pull/18186