[css-inline] Apply baseline-shift to inline-level boxes per dbaron's comment in today's telecon

Author: fantasai

css-inline/Overview.bs

@@ -244,7 +244,8 @@ Alignment Shift: 'baseline-shift' longhand</h4>
 	Name: baseline-shift
 	Value: <<length>> | <<percentage>> | sub | super
 	Initial: 0
-	Applies to: inline-level boxes
+	Applies to: inline-level boxes, flex items, grid items
+	<!-- table cells left out b/c CSS2.1 vertical-align values must have no effect... -->
 	Inherited: no
 	Percentages: refer to the used value of 'line-height'
 	Media: visual