[css-shapes-2]: shape(): using instead of via, allow any order in arcs/curves

Closes #5841

Author: noamr

css-shapes-2/Overview.bs

@@ -168,10 +168,10 @@ The ''shape()'' Function</h4>
 		<<move-command>> = move <<by-to>> <<coordinate-pair>>
 		<<line-command>> = line <<by-to>> <<coordinate-pair>>
 		<<hv-line-command>> = [hline | vline] <<by-to>> <<length-percentage>>
-		<<curve-command>> = curve <<by-to>> <<coordinate-pair>> via <<coordinate-pair>>{1,2}
-		<<smooth-command>> = smooth <<by-to>> <<coordinate-pair>> [via <<coordinate-pair>>]?
-		<<arc-command>> = arc <<by-to>> <<coordinate-pair>> of <<length-percentage>>{1,2}
-		                    [ <<arc-sweep>> || <<arc-size>> || rotate <<angle>> ]?
+		<<curve-command>> = curve [<<by-to>> <<coordinate-pair>> using <<coordinate-pair>>{1,2}]
+		<<smooth-command>> = smooth [[<<by-to>> <<coordinate-pair>>] || [using <<coordinate-pair>>]?]
+		<<arc-command>> = arc [[<<by-to>> <<coordinate-pair>>] || [of <<length-percentage>>{1,2}] ||
+		                        <<arc-sweep>>? || <<arc-size>>? || [rotate <<angle>>]?]
 		<<arc-sweep>> = cw | ccw
 		<<arc-size>> = large | small
 	</pre>