[css-text] Redefine text-wrap: balance in terms of remaining space. Probably needs better linkification at some point, but this'll do as a start.

Author: fantasai

css-text-4/Overview.bs

@@ -234,20 +234,17 @@ Text Wrap Settings: the 'text-wrap' property</h3>
 			For block-level elements that
 			contain line boxes as direct children,
 			line breaks are chosen to balance
-			the <a>inline-size</a> those line boxes consume,
+			the remaining (empty) space in each line box,
 			if better balance than ''text-wrap/normal'' is possible.
 			This must not change the number of line boxes
 			the block would contain
 			if 'text-wrap' were set to ''text-wrap/normal''.
 
-			For balancing purposes,
-			the <a>inline-size</a> to consider includes
-			any length taken up
-			by floats that shorten the line box.
-			The <a>inline-size</a> to consider comes before
-			any adjustments for justification.
+			The remaining space to consider
+			is that which remains after placing floats and inline content,
+			but before any adjustments due to text justification.
 			Line boxes are balanced when the standard deviation
-			from the average <a>inline-size</a> consumed
+			from the average <a>inline-size</a> of the remaining space in eacn line box
 			is reduced over the block
 			(including lines that end in a forced break).