[css-text-3] Fix handling of Emoji in line break transformation rules per #337 (comment) (Emoji are weirdly inconsistent in how they're classified according to EAW.)

Author: fantasai

css-text-3/Overview.bs

@@ -759,21 +759,26 @@ Characters and Letters</h3>
         <li>Otherwise, if the <a>East Asian Width property</a> [[!UAX11]] of both
           the character before and after the segment break is <code>F</code>,
           <code>W</code>, or <code>H</code> (not <code>A</code>),
-          and neither side is Hangul or Emoji (Unicode property <code>Emoji</code>),
+          and neither side is Hangul,
           then the segment break is removed.
         <li>Otherwise, if the <a>writing system</a> of the <a>segment break</a>
           is <a for=writing-system>Chinese</a>, <a for=writing-system>Japanese</a>, or Yi,
           and the character before or after the segment break
           is punctuation or a symbol (Unicode <a>general category</a> P* or S*)
-          and has an <a>East Asian Width property</a> of <code>A</code>
-          or is Emoji,
+          and has an <a>East Asian Width property</a> of <code>A</code>,
           and the character on the other side of the segment break is
           <code>F</code>, <code>W</code>, or <code>H</code>,
-          and not Hangul or Emoji,
+          and not Hangul,
           then the segment break is removed.
         <li>Otherwise, the segment break is converted to a space (U+0020).
       </ul>
 
+      <p>
+        For this purpose,
+        Emoji (Unicode property <code>Emoji</code>)
+        with an <a>East Asian Width property</a> of <code>W</code> or <code>N</code>
+        are treated as having an <a>East Asian Width property</a> of <code>A</code>.
+
       <p class="note">Note: The white space processing rules have already
         removed any tabs and spaces after the segment break before these checks
         take place.</p>