[css-text-3] Replace   with 　 in sample rendering pre blocks

  is used as a 1em wide spacer, but it doesn't (reliably) work,
since (at least on some platforms, such as OS X)   in a monospace font
gets squeezed to 1ch, to preserve the monospacing.
The ideographic space is also 1em wide, but doesn't get squeezed,
so use that instead.

Author: frivoal

css-text-3/Overview.bs

@@ -1939,12 +1939,12 @@ Word Spacing: the 'word-spacing' property</h3>
 
       &lt;p>abc&lt;/p></pre>
 
-    <p class="ls-ex good ls-fixed-width color-box" style="text-align: left">a&emsp;b&emsp;c</p>
-    <p class="ls-ex good ls-fixed-width color-box" style="text-align: right">a&emsp;b&emsp;c</p>
+    <p class="ls-ex good ls-fixed-width color-box" style="text-align: left">a&#x3000;b&#x3000;c</p>
+    <p class="ls-ex good ls-fixed-width color-box" style="text-align: right">a&#x3000;b&#x3000;c</p>
 
     <p>UAs therefore must not append letter spacing to the right or trailing edge of a line:</p>
 
-    <p class="ls-ex bad ls-fixed-width color-box" style="text-align: right">a&emsp;b&emsp;c&emsp;</p>
+    <p class="ls-ex bad ls-fixed-width color-box" style="text-align: right">a&#x3000;b&#x3000;c&#x3000;</p>
   </div>
 
     <p>Letter spacing between two <a>typographic character units</a> effectively “belongs”
@@ -1963,7 +1963,7 @@ Word Spacing: the 'word-spacing' property</h3>
 
       &lt;p>a&lt;span>bb&lt;/span>c&lt;/p></pre>
 
-    <p class="ls-ex">a&emsp;<span class="color-box">b&emsp;&emsp;b</span>&emsp;c</p>
+    <p class="ls-ex">a&#x3000;<span class="color-box">b&#x3000;&#x3000;b</span>&#x3000;c</p>
 
     <p>This also means that applying 'letter-spacing' to
     an element containing only a single character
@@ -1975,7 +1975,7 @@ Word Spacing: the 'word-spacing' property</h3>
 
       &lt;p>a&lt;span>b&lt;/span>c&lt;/p></pre>
 
-    <p class="ls-ex">a&emsp;<span class="color-box">b</span>&emsp;c</p>
+    <p class="ls-ex">a&#x3000;<span class="color-box">b</span>&#X3000;c</p>
 
     <p>An inline box only includes
     letter spacing between characters completely contained within that element:
@@ -1985,11 +1985,11 @@ Word Spacing: the 'word-spacing' property</h3>
 
       &lt;p>a&lt;span>bb&lt;/span>c&lt;/p></pre>
 
-    <p class="ls-ex good">a&emsp;<span class="color-box">b&emsp;b</span>&emsp;c</p>
+    <p class="ls-ex good">a&#x3000;<span class="color-box">b&#x3000;b</span>&#x3000;c</p>
 
     <p>It is incorrect to include the letter spacing on the right or trailing edge of the element:
 
-    <p class="ls-ex bad">a&emsp;<span class="color-box">b&emsp;b&emsp;</span>c</p>
+    <p class="ls-ex bad">a&#x3000;<span class="color-box">b&#x3000;b&#x3000;</span>c</p>
 
     <p>Letter spacing is inserted <strong>after</strong> RTL reordering,
     so the letter spacing applied to the inner span below has no effect,
@@ -2002,7 +2002,7 @@ Word Spacing: the 'word-spacing' property</h3>
       &lt;!-- Reordering will display these in reverse order. --&gt;
       <bdo dir=ltr>&lt;p>ab&lt;span>c&#x5d0;&lt;/span>&#x5d1;&#x5d2;&lt;/p></bdo></pre>
 
-    <p class="ls-ex">a&emsp;b</span>&emsp;<span class="color-box">c</span>&emsp;<span class="color-box">&#x5d0;</span>&emsp;&#x5d1;&emsp;&#x5d2;</p>
+    <p class="ls-ex">a&#x3000;b</span>&#x3000;<span class="color-box">c</span>&#x3000;<span class="color-box">&#x5d0;</span>&#x3000;&#x5d1;&#x3000;&#x5d2;</p>
   </div>
 
     <p>Letter spacing ignores invisible zero-width formatting characters