type: Allow symbol lists in .type.ensureSymbol

[kylenarocroc]

.type.ensureSymbol works on lists of strings and would be useful to allow it to work on lists of symbols

q).type.ensureSymbol ("abc";"def")
`abc`def
q).type.ensureSymbol `abc`def
'type
  [6]  src/kdb-common/src/type.q:134: .type.ensureSymbol:
    :`$x;
      ^
 }

with this change it becomes

q).type.ensureSymbol ("abc";"def")
`abc`def
q).type.ensureSymbol `abc`def
`abc`def