[css-inline-3] Make sure linegap metric is considered half-leading so it hooks into leading-trim properly.

Author: fantasai

css-inline-3/Overview.bs

@@ -408,6 +408,7 @@ Baseline Types and Metrics</h3>
 			Corresponds to the line-under ink edge of CJK (Han/Hangul/Kana) text.
 			Assigned <code>icfb</code> in OpenType.
 
+
 		<dt><dfn lt="hanging baseline" local-lt="hanging">hanging</dfn>
 		<dd>
 			Corresponds to hanging baseline
@@ -1107,7 +1108,7 @@ Logical Height Contributions of Inline Boxes</h3>
 	or this is the [=root inline box=],
 	the font’s [=line gap metric=]
 	may also be incorporated into <var>A</var> and <var>D</var>
-	by adding half to each side.
+	by adding half to each side as [=half-leading=].
 
 	When its computed 'line-height' is ''line-height/normal'',
 	the [=layout bounds=] of an inline box encloses all its glyphs,