[bindings] Compact ConstantConfiguration by using |union|

Source/bindings/templates/constants.cpp

 {##############################################################################}
 {% macro constant_getter_callback(constant) %}
 {% filter conditional(constant.conditional_string) %}
 static void {{constant.name}}ConstantGetterCallback(v8::Local<v8::Name>, const v8::PropertyCallbackInfo<v8::Value>& info)
 {
     TRACE_EVENT_SET_SAMPLING_STATE("blink", "DOMGetter");
     {% if constant.deprecate_as %}
     UseCounter::countDeprecationIfNotPrivateScript(info.GetIsolate(), callingExecutionContext(info.GetIsolate()), UseCounter::{{constant.deprecate_as}});
     {% endif %}
     {% if constant.measure_as %}
@@ skipping 42 matching lines @@
 static_assert({{constant.value}} == {{constant_cpp_class}}::{{constant.reflected_name}}, "the value of {{cpp_class}}_{{constant.reflected_name}} does not match with implementation");
 {% endif %}
 {% endfor %}
 {% endif %}
 {% endmacro %}
 
 
 {######################################}
 {%- macro constant_configuration(constant) %}
 {% if constant.idl_type in ('Double', 'Float') %}
-    {% set value = '0, %s, 0' % constant.value %}
+    {% set value = '%sf' % constant.value %}
 {% elif constant.idl_type == 'String' %}
-    {% set value = '0, 0, "%s"' % constant.value %}
+    {% set value = '"%s"' % constant.value %}
 {% else %}
     {# 'Short', 'Long' etc. #}
-    {% set value = '%s, 0, 0' % constant.value %}
+    {% set value = '%s' % constant.value %}
 {% endif %}
 {"{{constant.name}}", {{value}}, V8DOMConfiguration::ConstantType{{constant.idl_type}}}
 {%- endmacro %}