Introduce a bunch of small new headers (#1649)

* regs.h

* gfxalloc.h

* z64inventory.h

* gfx.h

* graph.h

* z64olib.h

* z64elf_message.h

* fix missing include

* Include z64inventory.h on z64save.h

* fix bss

* Move PosRot to z64math.h

* So dumb

* Update src/overlays/actors/ovl_En_Kusa/z_en_kusa.c

Co-authored-by: Derek Hensley <hensley.derek58@gmail.com>

* review

* Remove graph.h

* bss

---------

Co-authored-by: Derek Hensley <hensley.derek58@gmail.com>

src/code/z_camera.c

@@ -43,12 +43,17 @@
  *
  */
 
+#include "z64camera.h"
+
 #include "global.h"
 #include "string.h"
+
 #include "z64malloc.h"
+#include "z64olib.h"
 #include "z64quake.h"
 #include "z64shrink_window.h"
 #include "z64view.h"
+
 #include "overlays/actors/ovl_En_Horse/z_en_horse.h"
 
 void func_800DDFE0(Camera* camera);