Amend definition of motion animation to *not* exclude blurring (#4040)

Closes #3949

<!--
    This comment and the below content is programmatically generated.
    You may add a comma-separated list of anchors you'd like a
    direct link to below (e.g. #idl-serializers, #idl-sequence):

    Don't remove this comment or modify anything below this line.
    If you don't want a preview generated for this pull request,
    just replace the whole of this comment's content by "no preview"
    and remove what's below.
-->
***
<a href="https://pr-preview.s3.amazonaws.com/w3c/wcag/pull/4040.html"
title="Last updated on Oct 4, 2024, 3:07 PM UTC (abe30f6)">Preview</a> |
<a
href="https://pr-preview.s3.amazonaws.com/w3c/wcag/4040/a9e49c0...abe30f6.html"
title="Last updated on Oct 4, 2024, 3:07 PM UTC (abe30f6)">Diff</a>

---------

Co-authored-by: Mike Gower <[email protected]>
Co-authored-by: Alastair Campbell <[email protected]>
Co-authored-by: James Craig <[email protected]>
(cherry picked from commit 342b58e)

Author: 4 people

guidelines/terms/21/motion-animation.html

@@ -1,7 +1,5 @@
 <dt><dfn id="dfn-motion-animation">motion animation</dfn></dt>
 <dd>
-   					
    <p>addition of steps between conditions to create the illusion of movement or to give a sense of a smooth transition</p>
-	<aside class="example"><p>For example, an element which moves into place or changes size while appearing is considered to be animated. An element which appears instantly without transitioning is not using animation. Motion animation does not include changes of color, blurring, or opacity which do not change the perceived size, shape, or position of the element.</p></aside>
-   				
+	<aside class="example"><p>For example, an element which moves into place or changes size while appearing is considered to be animated. An element which appears or changes instantly, without transition/animation steps, is not using animation.</p><p>Motion animation does not include changes – such as changes of color or opacity – that do not alter the perceived size, shape, position, or distance/depth of the element to the viewer.</p></aside>
 </dd>