RFR: 7046: Update to the 2021-03 platform

Fri Apr 2 00:11:33 UTC 2021

Also updating to latest babel for the platform versions that are available in 0.18.3.

Depending on if #234 gets in before or after this one, either this one will need to be updated to remove the chromium entry, or #234 will need to be updated to do it.

(Is it just me, or does JMC start really fast on 4.19? :) )

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Commit messages:
 - 7046: Update to the 2021-03 platform

Changes: https://git.openjdk.java.net/jmc/pull/235/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=235&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-7046
  Stats: 110 lines in 6 files changed: 93 ins; 3 del; 14 mod
  Patch: https://git.openjdk.java.net/jmc/pull/235.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/235/head:pull/235

PR: https://git.openjdk.java.net/jmc/pull/235