RFR: 8276794: Change nested classes in java.desktop to static nested classes

[Andrey Turbanov]

Non-static classes hold a link to their parent classes, which in many cases can be avoided.
I updated only private and package-private classes. Didn't touch public/protected to not break external code.
Similar cleanup in java.base - [JDK-8261880](https://bugs.openjdk.java.net/browse/JDK-8261880)

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Commit messages:
 - [PATCH] Change nested classes in java.desktop to static nested classes

Changes: https://git.openjdk.java.net/jdk/pull/5943/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5943&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276794
  Stats: 219 lines in 79 files changed: 3 ins; 47 del; 169 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5943.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5943/head:pull/5943

PR: https://git.openjdk.java.net/jdk/pull/5943