RFR: 8286037: Bump minimum boot jdk to JDK 19

[Mikael Vidstedt]

With the JDK 19 GA out it's time to bump the minimum boot JDK version for mainline/JDK 20.

Testing: tier1-5, GHA builds

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Commit messages:
 - Fix URLs
 - 8286037: Bump minimum boot jdk to JDK 19

Changes: https://git.openjdk.org/jdk/pull/10564/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10564&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8286037
  Stats: 8 lines in 3 files changed: 0 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/10564.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10564/head:pull/10564

PR: https://git.openjdk.org/jdk/pull/10564