RFR: JDK-8284928: Add links from SourceVersion to specific JLS versions [v2]

[Joe Darcy]

> As a convenience to readers, add links from the SourceVersion constants to the particular JLS release they correspond to.

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-8284928
 - JDK-8284928: Add links from SourceVersion to specific JLS versions

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8275/files
  - new: https://git.openjdk.java.net/jdk/pull/8275/files/08577a28..984ae7da

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8275&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8275&range=00-01

  Stats: 122 lines in 12 files changed: 55 ins; 17 del; 50 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8275.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8275/head:pull/8275

PR: https://git.openjdk.java.net/jdk/pull/8275