String.setChar

Replace a single character at $index.

If $index is negative, it counts from the end of the string.

The index must be inside the bounds of the string.

'abcdef'.setChar(1, 'X')
//= 'Xbcdef'

'abcdef'.setChar(3, 'X')
//= 'abXdef'

'abcdef'.setChar(-1, 'X')
//= 'abcdeX'

'abcdef'.setChar(100, 'X')
//= ERROR