RFR: JDK-8284966: Update SourceVersion.RELEASE_19 description for language changes [v2]

[Joe Darcy]

> Updating the description of RELEASE_19 for the anticipated language changes in Java SE 19. I'll defer pushing until the proposed-to-target record patterns compiler changes are pushed. Also adding links to the JSR 269 API in the package info files.

Joe Darcy has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'master' into JDK-8284966
 - JDK-8284966: Update SourceVersion.RELEASE_19 description for language changes

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8793/files
  - new: https://git.openjdk.java.net/jdk/pull/8793/files/98977554..6df77a29

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8793&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8793&range=00-01

  Stats: 38164 lines in 650 files changed: 8903 ins; 27617 del; 1644 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8793.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8793/head:pull/8793

PR: https://git.openjdk.java.net/jdk/pull/8793