Everywhere: Replace single-char StringView op. arguments with chars

This prevents us from needing a sv suffix, and potentially reduces the
need to run generic code for a single character (as contains,
starts_with, ends_with etc. for a char will be just a length and
equality check).

No functional changes.

Userland/Libraries/LibWeb/CSS/Parser/Function.cpp

@@ -23,9 +23,9 @@ String Function::to_string() const
     StringBuilder builder;
 
     serialize_an_identifier(builder, m_name);
-    builder.append("(");
-    builder.join(" ", m_values);
-    builder.append(")");
+    builder.append('(');
+    builder.join(' ', m_values);
+    builder.append(')');
 
     return builder.to_string();
 }