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/compile.h

@@ -30,6 +30,9 @@
 #include "py/parse.h"
 #include "py/emitglue.h"
 
+// Whether mp_compile_to_raw_code is exposed as a public function.
+#define MICROPY_EXPOSE_MP_COMPILE_TO_RAW_CODE (MICROPY_PY_BUILTINS_CODE >= MICROPY_PY_BUILTINS_CODE_BASIC || MICROPY_PERSISTENT_CODE_SAVE)
+
 #if MICROPY_COMP_ALLOW_TOP_LEVEL_AWAIT
 // set to `true` to allow top-level await expressions
 extern bool mp_compile_allow_top_level_await;
@@ -40,7 +43,7 @@ extern bool mp_compile_allow_top_level_await;
 // mp_globals_get() will be used for the context
 mp_obj_t mp_compile(mp_parse_tree_t *parse_tree, qstr source_file, bool is_repl);
 
-#if MICROPY_PERSISTENT_CODE_SAVE
+#if MICROPY_EXPOSE_MP_COMPILE_TO_RAW_CODE
 // this has the same semantics as mp_compile
 void mp_compile_to_raw_code(mp_parse_tree_t *parse_tree, qstr source_file, bool is_repl, mp_compiled_module_t *cm);
 #endif