Adjust text attachment drawing to account for fractional textContainer width

[willbur1984]

Within KSOTokenDefaultTextAttachment, attachmentBoundsForTextContainer:proposedLineFragment:glyphPosition:characterIndex: provides the maximum width for the text attachment on the current line given CGRectGetWidth(lineFrag) - glyphPosition.x. This should be taken into account when drawing the image, as a result the image should adjust its appearance to reveal more of the text it represents if more space becomes available on a given line.

The current implementation just assumes max width to be the width of the containing text view would put each large text attachment on its own line, which is not ideal.