[SuperIOSTextField] Update text selection handles sizing and layout to match native iOS design spec

[rutvik110]

SuperIOSTextField text selection handles doesn't follow the native iOS design specs as documented here. This includes the text selection handle bar and the circle that is shown above/below the handle.

Need to update following things to match the native behaviour:

• iOS uses handle circle radius of 6px under all circumstances. SuperIOSTextField currently uses 4px. Update that. read
• On iOS, the drag handle rectangles are exactly as tall as the selection highlight rectangle for a given line, and the top and bottom of those handle rectangles match the selection rectangle. Update the handle bar layout to match the native behaviour. read
• On iOS, the drag handle circle sits completely above/below the very top/bottom edge of the handle. SuperIOSTextField circle overlaps with the selection area. Update it. read