Electric char auto-indentation doesn't work with multiple cursors

[peterflynn]

Start with this:

if (foo) {
    |
if (bar) {
    |

1. Put a cursor where each '|' is (don't actually include the '|'s in the text)
2. Type '}'

Result: Only the last one is back-indented properly:

if (foo) {
    }
if (bar) {
}

This is because Editor._checkElectricChars() isn't multi-cursor aware.

[dangoor]

Reviewed medium priority to editor area. Called medium priority because one cursor may be off the screen and the user will be expecting consistent behavior between the cursors.

[prafulVaishnav]

Fixed by PR #9387