This commit scales the caret on a DPI change event on styled text. It
uses the line height of the styled text to set on caret. The
height and width field in the caret are storing data in points now and
not in pixels. We do so to avail the scaling refernece. Also we use
SWT.DEFAULT to ignore setting of width. It is useful when we set the new
height on DPI change since the preferred width of the caret is loadeed
from preferences on the Caret creation.

Contributes to #62 and #127