RFR: 6909: Upgrade to Eclipse 2020-09

[Marcus Hirt]

Adds the Eclipse 2020-09 platform, upgrades 2020-09 and 2020-06 to use the 2020-06 babel bundles, and sets 2020-09 to
be the default.

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Commit messages:
 - Adding Eclipse project
 - 6909: Upgrade to Eclipse 2020-09

Changes: https://git.openjdk.java.net/jmc/pull/111/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=111&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-6909
  Stats: 94 lines in 6 files changed: 82 ins; 1 del; 11 mod
  Patch: https://git.openjdk.java.net/jmc/pull/111.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/111/head:pull/111

PR: https://git.openjdk.java.net/jmc/pull/111