RFR: 7509: Add 2021-09 target platform

[Marcus Hirt]

...also updating babel.

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Commit messages:
 - 7509: Add 2021-09 target platform
 - Fixing copyright years
 - Further project files and fixes
 - 7505: Fixing project setup

Changes: https://git.openjdk.java.net/jmc/pull/357/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=357&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-7509
  Stats: 352 lines in 39 files changed: 199 ins; 12 del; 141 mod
  Patch: https://git.openjdk.java.net/jmc/pull/357.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/357/head:pull/357

PR: https://git.openjdk.java.net/jmc/pull/357