Replace <geometry-box> with <coord-box> mask-origin & mask-clip (w3c#525)

This edit should have been part of w3c#5.

Fixes w3c#439.

Author: FormularSumo

css-masking-1/Overview.bs

@@ -617,7 +617,7 @@ See the section <a href="#layering">“Layering multiple mask layer images”</a
 
 <pre class=propdef>
 Name: mask-clip
-Value: [ <<geometry-box>> | no-clip ]#
+Value: [ <<coord-box>> | no-clip ]#
 Initial: border-box
 Applies to: All elements. In SVG, it applies to <a>container elements</a> excluding the <a element>defs</a> element, all <a>graphics elements</a> and the <a element>use</a> element
 Inherited: no
@@ -667,7 +667,7 @@ See the section <a href="#layering">“Layering multiple mask layer images”</a
 
 <pre class=propdef>
 Name: mask-origin
-Value: <<geometry-box>>#
+Value: <<coord-box>>#
 Initial: border-box
 Applies to: All elements. In SVG, it applies to <a>container elements</a> excluding the <a element>defs</a> element, all <a>graphics elements</a> and the <a element>use</a> element
 Inherited: no