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/LibJS/Bytecode/Op.cpp

@@ -1030,7 +1030,7 @@ String PushDeclarativeEnvironment::to_string_impl(Bytecode::Executable const& ex
         Vector<String> names;
         for (auto& it : m_variables)
             names.append(executable.get_string(it.key));
-        builder.append("}");
+        builder.append('}');
         builder.join(", "sv, names);
     }
     return builder.to_string();