[project] Generate syscalls from new interface DSL

This change adds a new interface DSL for specifying objects (with
methods) and interfaces (that expose objects, and optionally have their
own methods).

Significant changes:

- Add the new scripts/definitions Python module to parse the DSL
- Add the new definitions directory containing DSL definition files
- Use cog to generate syscall-related code in kernel and libj6
- Unify ordering of pointer + length pairs in interfaces

scripts/definitions/templates/syscall/client/public/syscalls.h

@@ -0,0 +1,25 @@
+#pragma once
+
+#include <j6/types.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+{% macro argument(type, name, first, options=False) -%}
+    {%- for ctype, suffix in type.c_names(options) -%}
+        {%- if not first or not loop.first %}, {% endif %}{{ ctype }} {{ name }}{{ suffix }}
+    {%- endfor -%}
+{%- endmacro %}
+ 
+{% for id, scope, method in interface.methods %}
+j6_status_t __syscall_{% if scope %}{{ scope.name }}_{% endif %}{{ method.name }} (
+    {%- if not method.static -%}{{ argument(scope.reftype, "self", True) }}{% endif -%}
+    {%- set first = method.static -%}
+    {%- for param in method.params %}{{ argument(param.type, param.name, first, options=param.options) }}{% set first = False %}{% endfor -%}
+);
+{% endfor %}
+
+#ifdef __cplusplus
+}
+#endif
+