RFR: JDK-8309554: Update descriptions in SourceVersion

[Joe Darcy]

Update SourceVersion to user terminology under consideration for the related ClassFileFormatVersion enum, changing "recognized by" to "introduced by".

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

Commit messages:
 - JDK-8309554: Update descriptions in SourceVersion

Changes: https://git.openjdk.org/jdk/pull/14340/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14340&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309554
  Stats: 29 lines in 1 file changed: 4 ins; 0 del; 25 mod
  Patch: https://git.openjdk.org/jdk/pull/14340.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14340/head:pull/14340

PR: https://git.openjdk.org/jdk/pull/14340