Fix a stale Ignore and its own test bug on an already-working ::after test

CssContentWithCssEscapeInString_RendersLiterally was Ignore'd, citing
"this fork has no pseudo-element support at all" - false: ::before
already works (the CSS-escape test right above it in this same file
passes), and CssContentEngine/CssData's pseudo-element creation
predates this port entirely.

Un-ignoring it surfaced a real bug in the TEST itself, not the
engine: its box-finding predicate (HtmlTag == null && Text != null)
matches the real text node "text" (which also has no HtmlTag) before
it reaches the ::after box, since ::after is appended at the end of
p.Boxes while ::before is inserted at index 0 - the sibling test just
above happens to pass because ::before's insert-at-0 placement wins
the FirstOrDefault race by coincidence. Fixed to key off
IsAfterPseudoElement directly, and it passes.

Author: jhaygood86

Source/Test/HtmlRenderer.IntegrationTest/Text/HtmlEntityDecodingIntegrationTests.cs

@@ -189,9 +189,6 @@ public void CssContentWithCssEscape_RendersLiterally()
         Assert.AreEqual("&", beforeBox!.Text);
     }
 
-    [Ignore("Requires ::before/::after pseudo-elements with a CSS content: property - this fork has no " +
-            "pseudo-element support at all (confirmed: no \"::before\"/\"::after\"/pseudo-element handling " +
-            "anywhere in Core, only :link/:hover pseudo-CLASSES are recognized).")]
     [TestMethod]
     public void CssContentWithCssEscapeInString_RendersLiterally()
     {
@@ -200,7 +197,10 @@ public void CssContentWithCssEscapeInString_RendersLiterally()
         var (root, _) = LayoutHarness.Layout(html);
         var p = LayoutHarness.FindById(root, "p")!;
 
-        var afterBox = p.Boxes.FirstOrDefault(b => b.HtmlTag == null && b.Text != null);
+        // Unlike ::before (inserted at index 0), ::after is appended at the end of p.Boxes - so
+        // FirstOrDefault(HtmlTag == null) would instead match the real text node "text" (which also has
+        // no HtmlTag), not the pseudo box. IsAfterPseudoElement identifies it unambiguously.
+        var afterBox = p.Boxes.FirstOrDefault(b => b.IsAfterPseudoElement);
         Assert.IsNotNull(afterBox);
         Assert.IsTrue(afterBox!.Text!.Contains('<'));
         Assert.IsTrue(afterBox.Text!.Contains('>'));