RFR: 8238173: jshell - switch statement with a single default not return cause syntax error

[Jan Lahoda]

Improving disambiguation between switch expressions and switch statements: switches that do not yield a value from any arm should not be considered switch expressions; switches in source levels that don't support switch expressions should always be considered switch statements.

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

Commit messages:
 - 8238173: jshell - switch statement with a single default not return cause syntax error

Changes: https://git.openjdk.java.net/jdk/pull/3173/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3173&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8238173
  Stats: 56 lines in 5 files changed: 32 ins; 22 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3173.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3173/head:pull/3173

PR: https://git.openjdk.java.net/jdk/pull/3173