py/objcode: Factor code object out into its own file.

The `mp_obj_code_t` and `mp_type_code` code object was defined internally
in both `py/builtinevex.c` and `py/profile.c`, with completely different
implementations (the former very minimal, the latter quite complete).

This commit factors these implementations into a new, separate source file,
and allows the code object to have four different modes, selected at
compile-time:

- MICROPY_PY_BUILTINS_CODE_NONE: code object not included in the build.

- MICROPY_PY_BUILTINS_CODE_MINIMUM: very simple code object that just holds
  a reference to the function that it represents.  This level is used when
  MICROPY_PY_BUILTINS_COMPILE is enabled.

- MICROPY_PY_BUILTINS_CODE_BASIC: simple code object that holds a reference
  to the proto-function and its constants.

- MICROPY_PY_BUILTINS_CODE_FULL: almost complete implementation of the code
  object.  This level is used when MICROPY_PY_SYS_SETTRACE is enabled.

Signed-off-by: Damien George <damien@micropython.org>

py/runtime.c

@@ -1620,10 +1620,13 @@ mp_obj_t mp_parse_compile_execute(mp_lexer_t *lex, mp_parse_input_kind_t parse_i
     mp_obj_t module_fun = mp_compile(&parse_tree, source_name, parse_input_kind == MP_PARSE_SINGLE_INPUT);
 
     mp_obj_t ret;
-    if (MICROPY_PY_BUILTINS_COMPILE && globals == NULL) {
+    #if MICROPY_PY_BUILTINS_COMPILE && MICROPY_PY_BUILTINS_CODE == MICROPY_PY_BUILTINS_CODE_MINIMUM
+    if (globals == NULL) {
         // for compile only, return value is the module function
         ret = module_fun;
-    } else {
+    } else
+    #endif
+    {
         // execute module function and get return value
         ret = mp_call_function_0(module_fun);
     }