IconPackHelper: Respect the original size of bitmap icons

When use icon packs on low-resolution devices, for example, my HDPI
phone, it seems that using the size returned by
getLauncherLargeIconSize() will cause a blurness on
some icons that are not included in the icon pack because of the compose
function.

This patch respects the original size of the icon if the icon is an
instance of BitmapDrawable but use the size returned by
getLauncherLargeIconSize() if the icon is an instance of PaintDrawable.
This will remove icon blurness on low-resolution devices.

Change-Id: Ifcb39020d934a9c7cb409e1206a179d64f99aa37