Issue Description:

Steps to reproduce:

• Open the swift repl (swift)

• Type something that uses fullwidth characters (let hello = "こんにちは")

• Press Enter

• Press up arrow to go back to the previous line

The cursor will now be in the middle of the string instead of at the end. Typing will visually overwrite pieces of the string (though it will be treated as if it were at the end from the standpoint of executing commands in the repl).