Don't insert extra close bracket when the cursor is already on top of one

[byorgey]

With #1953 , at the REPL we now automatically insert a matching close bracket when typing an open paren, square bracket, or curly brace. To go along with this, it would be nice if the REPL did not insert an extra close bracket when you type one but the cursor is already on top of one --- it should just move the cursor one space to the right instead.

For example, suppose you type open paren, x, +, y, close paren. Right now you would end up with

(x+y)|)

(where | indicates the cursor position) but I would like to end up with

(x+y)|