Commonly referred to as an ‘Apron’. Don’t think I’ve ever heard it referred to as ‘Taper’, (even though that is what it is).
The Graphic is correct. The apron is beyond the taper.
Not in my area. The garage slab comes to a vertical edge just beyond the door seal, and the taper is part of the apron, if there is an apron or taper at all.
What degree should the slope be?
About the same slope as a window sill, 7 degrees
I don’t think I have ever seen this in the field. Pretty much always see them like the photo from Mr. Jonas.