LibWeb: Ignore backslashes (\) in attribute selectors

This makes us at least parse selectors like [foo=bar\ baz] correctly.
The current solution here is quite hackish but the real fix will come
when we implement a spec-compliant CSS parser.

Libraries/LibWeb/Parser/CSSParser.cpp

@@ -492,6 +492,9 @@ public:
                     }
                     continue;
                 }
+                // FIXME: This is a hack that will go away when we replace this with a big boy CSS parser.
+                if (ch == '\\')
+                    ch = consume_one();
                 buffer.append(ch);
             }
             if (in_value)