RFR: 8286206: Missing cases for RECORD

[Jan Lahoda]

Adds handling of `ElementKind.RECORD` to JShell's code completion.

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Commit messages:
 - 8286206: Missing cases for RECORD

Changes: https://git.openjdk.java.net/jdk/pull/9042/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=9042&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286206
  Stats: 40 lines in 3 files changed: 31 ins; 0 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk/pull/9042.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/9042/head:pull/9042

PR: https://git.openjdk.java.net/jdk/pull/9042