Add short options into valid tokens

- Add short options as valid tokens in a `CommandModel` so that Lexer
  create tokens with accurate info and doesn't then cascade this issue
  in Ast and Parser.
- Previously with a command `command -a aaa -b bbb` tokenisation resulted
  `COMMAND OPTION ARGUMENT ARGUMENT ARGUMENT` with multiple short options
  while it should have been `COMMAND OPTION ARGUMENT OPTION ARGUMENT`.
- Relates #757

spring-shell-core/src/main/java/org/springframework/shell/command/parser/CommandModel.java

@@ -196,6 +196,9 @@ public class CommandModel {
 					for (String longName : commandOption.getLongNames()) {
 						tokens.put("--" + longName, new Token(longName, TokenType.OPTION));
 					}
+					for (Character shortName : commandOption.getShortNames()) {
+						tokens.put("-" + shortName, new Token(shortName.toString(), TokenType.OPTION));
+					}
 				});
 			}
 			return tokens;