RFR: 8372850: Update comment in SourceVersion for language evolution history for changes in 26

[Joe Darcy]

Include source-level comments about per-release language changes, or lack thereof.

-------------

Commit messages:
 - JDK-8372850: Update comment in SourceVersion for language evolution history for changes in 26

Changes: https://git.openjdk.org/jdk/pull/28594/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28594&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372850
  Stats: 6 lines in 1 file changed: 6 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/28594.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28594/head:pull/28594

PR: https://git.openjdk.org/jdk/pull/28594