[css-contain] Move interaction with overflow-clip-margin to L2

Part of #4934

Author: frivoal

css-contain-1/Overview.bs

@@ -733,10 +733,6 @@ Paint Containment</h3>
 		nor does it inhibit the creation of any such mechanism through other properties,
 		<span class=informative>such as 'overflow', 'resize', or 'text-overflow'</span>.
 
-		This clipping shape respects 'overflow-clip-margin',
-		allowing an element with [=paint containment=]
-		to still slightly overflow its normal bounds.
-
 		Note: The behavior is described in this paragraph is equivalent to changing
 		''overflow-x: visible'' into ''overflow-x: clip''
 		and

css-contain-2/Overview.bs

@@ -880,6 +880,10 @@ Paint Containment</h3>
 		nor does it inhibit the creation of any such mechanism through other properties,
 		<span class=informative>such as 'overflow', 'resize', or 'text-overflow'</span>.
 
+		This clipping shape respects 'overflow-clip-margin',
+		allowing an element with [=paint containment=]
+		to still slightly overflow its normal bounds.
+
 		Note: The behavior is described in this paragraph is equivalent to changing
 		''overflow-x: visible'' into ''overflow-x: clip''
 		and
@@ -1540,4 +1544,5 @@ Changes from <a href="https://www.w3.org/TR/css-contain-1/">CSS Containment Leve
 </h3>
 
 * Restored [=style containment=], which had been dropped from Level 1
+* Define the interaction between [=paint containment=] and 'overflow-clip-margin'