Mojo C++ bindings: expose public <struct>DataView and StringDataView.

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

 {% from "enum_macros.tmpl" import enum_decl -%}
 
 class {{struct.name}} {
  public:
   using Data_ = internal::{{struct.name}}_Data;
+
+  // TODO(yzshen): Remove Reader.
   using Reader = {{struct.name}}_Reader;
 
 {#--- Enums #}
 {%- for enum in struct.enums -%}
   {{enum_decl(enum)|indent(2)}}
 {%- endfor %}
 
 {#--- Constants #}
 {%- for constant in struct.constants %}
 {%-   if constant.kind|is_integral_kind %}
@@ skipping 39 matching lines @@
 {%  for field in struct.fields %}
 {%-   set type = field.kind|cpp_wrapper_type %}
 {%-   set name = field.name %}
   {{type}} {{name}};
 {%- endfor %}
 };
 
 {# TODO(yzshen): Redo the Reader interface. #}
 {# NOTE: Generated Reader instances are intentionally cheap to copy and devoid
    of heap allocations. They should stay this way. #}
+// TODO(yzshen): Remove this.
 class {{struct.name}}_Reader {
  public:
   {{struct.name}}_Reader(internal::{{struct.name}}_Data* data,
                          mojo::internal::SerializationContext* context);
 
 {%-   for pf in struct.packed.packed_fields_in_ordinal_order %}
 {%-     set kind = pf.field.kind -%}
 {%-     set name = pf.field.name -%}
 {%-     if kind|is_nullable_kind %}
   bool has_{{name}}() const;
@@ skipping 20 matching lines @@
   }
 {%-     else %}
   {{kind|cpp_result_type}} {{name}}() const { return data_->{{name}}; }
 {%-     endif %}
 {%-   endfor %}
 
  private:
   internal::{{struct.name}}_Data* data_;
   mojo::internal::SerializationContext* context_;
 };