RFR: 8212: Update trunk to 9.1.0

[Marcus Hirt]

Also EA splash and minor versioning fixes.

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Commit messages:
 - EA splash
 - Minor fixes
 - Update to 9.1.0

Changes: https://git.openjdk.org/jmc/pull/558/files
  Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=558&range=00
  Issue: https://bugs.openjdk.org/browse/JMC-8212
  Stats: 251 lines in 151 files changed: 0 ins; 0 del; 251 mod
  Patch: https://git.openjdk.org/jmc/pull/558.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/558/head:pull/558

PR: https://git.openjdk.org/jmc/pull/558