Fix PercentLiterDelimiters auto-correct

Make PercentLiterDelimiters preserve the indentation of the contained expression.
This feels like a bit too much effort for just replacing two characters in a string. Does anyone have a suggestion on how to improve it. The "problem" is that it is not known exactly which characters should be replaced (they could be any delimiter pair) nor the position of the last character (it could be followed by regular expression modifiers).