JShell: support for switch expressions

Switch expressions in statements appear to work fine, but they are not recognized as expressions. For example:

jshell> switch (day) {
   ...> case MONDAY, FRIDAY, SUNDAY -> 6;
   ...> case TUESDAY -> 7;
   ...> case THURSDAY, SATURDAY -> 8;
   ...> case WEDNESDAY -> 9;
   ...> }
| Error:
| not a statement
| case MONDAY, FRIDAY, SUNDAY -> 6;
| ^
| Error:
| not a statement
| case TUESDAY -> 7;
| ^
| Error:
| not a statement
| case THURSDAY, SATURDAY -> 8;
| ^
| Error:
| not a statement
| case WEDNESDAY -> 9;
| ^

This is due to "switch" triggering the statement path of code analysis and parsing.

Completion needs to be addressed as well. For example,

switch (day) {
           case MONDAY, FRIDAY, SUNDAY -> 6;
           case TUESDAY -> 7;
           case WEDNESDAY -> 9;
           case THURSDAY, SATURDAY -> 8;
       } + 100

does not include the "+ 100". This may be hard to address.

-Robert