RFR: 8257776: [valhalla:jep390] Add disclaimer about future changes to value-based classes [v4]

[Dan Smith]

> Addressing CSR feedback by mentioning the possibility of future behavioral changes to value-based classes.

Dan Smith has updated the pull request incrementally with one additional commit since the last revision:

  Wrap lines to <120 chars

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Changes:
  - all: https://git.openjdk.java.net/valhalla/pull/294/files
  - new: https://git.openjdk.java.net/valhalla/pull/294/files/f35d5acf..a51ee1a1

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=valhalla&pr=294&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=valhalla&pr=294&range=02-03

  Stats: 6 lines in 3 files changed: 0 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/294.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/294/head:pull/294

PR: https://git.openjdk.java.net/valhalla/pull/294