Implement the device error callback.

This adds support for "natively defined" API types like callbacks that
will have to be implemented manually for each target language. Also this
splits the concept of "native method" into a set of native methods per
language.

Removes the "Synchronous error" concept that was used to make builders
work in the maybe Monad, this will have to be reinroduced with builder
callbacks.

generator/templates/apicpp.cpp

@@ -64,7 +64,7 @@ namespace nxt {
                             {{as_varName(arg.name)}}.Get()
                         {%- elif arg.type.category == "enum" or arg.type.category == "bitmask" -%}
                             static_cast<{{as_cType(arg.type.name)}}>({{as_varName(arg.name)}})
-                        {%- elif arg.type.category == "native" -%}
+                        {%- elif arg.type.category in ["native", "natively defined"] -%}
                             {{as_varName(arg.name)}}
                         {%- else -%}
                             UNHANDLED
@@ -76,7 +76,7 @@ namespace nxt {
             )
         {%- endmacro %}
 
-        {% for method in type.methods %}
+        {% for method in native_methods(type) %}
             {{render_cpp_method_declaration(type, method)}} {
                 {% if method.return_type.name.concatcase() == "void" %}
                     {{render_cpp_to_c_method_call(type, method)}};