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

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

 {%- import "interface_macros.tmpl" as interface_macros %}
 {%- import "struct_macros.tmpl" as struct_macros %}
 
 {%- set class_name = interface.name %}
 {%- set proxy_name = interface.name ~ "Proxy" %}
 {%- set namespace_as_string = "%s"|format(namespace|replace(".","::")) %}
 
 {%- macro alloc_params(struct, params, message, serialization_context) %}
   ({{params}})->DecodePointers();
   ({{serialization_context}})->handles.Swap(({{message}})->mutable_handles());
   bool success = true;
 {%-   for param in struct.packed.packed_fields_in_ordinal_order %}
   {{param.field.kind|cpp_wrapper_type}} p_{{param.field.name}}{};
 {%-   endfor %}
-  {{struct_macros.deserialize(
-      struct, params, "p_%s", serialization_context, "success")}}
+  {{struct.name}}DataView input_data_view({{params}},
+                                          {{serialization_context}});
+  {{struct_macros.deserialize(struct, "input_data_view", "p_%s", "success")}}
   if (!success)
     return false;
 {%- endmacro %}
 
 {%- macro pass_params(parameters) %}
 {%-   for param in parameters %}
 {%-     if param.kind|is_move_only_kind -%}
 std::move(p_{{param.name}})
 {%-     else -%}
 p_{{param.name}}
@@ skipping 392 matching lines @@
     default:
       break;
   }
 
   // Unrecognized message.
   ReportValidationError(
       mojo::internal::VALIDATION_ERROR_MESSAGE_HEADER_UNKNOWN_METHOD);
   return false;
 }
 {%- endif -%}