RFR: 8355536: Create version constants to model preview language and vm features [v3]

[Chen Liang]

> Sometimes, for version-specific feature access APIs, we wish to access the preview features of the current Java SE release. To reduce the impact of adding one preview-specific version on every site, we can add a constant modeling the preview features as a fake version.

Chen Liang has updated the pull request incrementally with one additional commit since the last revision:

  Update src/java.compiler/share/classes/javax/lang/model/SourceVersion.java
  
  Co-authored-by: Luca Kellermann <lukellmann at gmail.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/25017/files
  - new: https://git.openjdk.org/jdk/pull/25017/files/d0ff022f..0a3f3896

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25017&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25017&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/25017.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25017/head:pull/25017

PR: https://git.openjdk.org/jdk/pull/25017