Mojo C++ bindings: extract code shared by different variants.

mojo/public/tools/bindings/generators/cpp_templates/struct_declaration.tmpl

 {%- set class_name = struct.name ~ "_Data" -%}
 
 class {{class_name}} {
  public:
   static {{class_name}}* New(mojo::internal::Buffer* buf) {
     return new (buf->Allocate(sizeof({{class_name}}))) {{class_name}}();
   }
 
   static bool Validate(const void* data,
                        mojo::internal::ValidationContext* validation_context);
 
-{% from "enum_macros.tmpl" import enum_data_decl -%}
-{#--- Enums #}
-{%- for enum in struct.enums -%}
-{%-   if enum|is_native_only_kind %}
-  using {{enum.name}}_Data = mojo::internal::NativeEnum_Data;
-{%-   else %}
-  {{enum_data_decl(enum)|indent(2)}}
-{%-   endif %}
-{%- endfor %}
-
   mojo::internal::StructHeader header_;
 {%- for packed_field in struct.packed.packed_fields %}
 {%-   set name = packed_field.field.name %}
 {%-   set kind = packed_field.field.kind %}
 {%-   if kind.spec == 'b' %}
   uint8_t {{name}} : 1;
 {%-   else %}
   {{kind|cpp_field_type}} {{name}};
 {%-   endif %}
 {%-   if not loop.last %}
@@ skipping 15 matching lines @@
 {%-   endif %}
 {%- endif %}
 
  private:
   {{class_name}}() : header_({sizeof(*this), {{struct.versions[-1].version}}}) {
   }
   ~{{class_name}}() = delete;
 };
 static_assert(sizeof({{class_name}}) == {{struct.versions[-1].num_bytes}},
               "Bad sizeof({{class_name}})");