[jfx15] RFR: 8249537: Update copyright header for files modified in 2020

[Ambarish Rapte]

Update last modified year of copyright headers for files modified in 2020.

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Commit messages:
 - 8249537: Update copyright header for files modified in 2020

Changes: https://git.openjdk.java.net/jfx/pull/281/files
 Webrev: https://webrevs.openjdk.java.net/jfx/281/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8249537
  Stats: 92 lines in 91 files changed: 0 ins; 0 del; 92 mod
  Patch: https://git.openjdk.java.net/jfx/pull/281.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/281/head:pull/281

PR: https://git.openjdk.java.net/jfx/pull/281