Split z64.h: move various things, state, sram, gfx, jpeg, prerender, speedmeter (#1487)

* Split z64.h more

* fix speedmeter.h (expect this kind of issue resolution to pop up eventually)

* fix z64object.h

* fix z64state.h

* fix (probably only partially) z64play.h

* fix fix speedmeter.h :)

* revert making a play header (sadge), add/split transition & transition_instances

* move stuff to cutscene, interface

* Move `TransitionCircle%` enums to `z64transition_instances.h`

* z64state.h -> z64game.h with a "this is not final" comment

* forward declare GraphicsContext in z64game.h instead of including the header file for it

* don't comment on where the forward declarations are from

reasoning:
1) it's easy to go out of sync (like this comment, it was outdated anyway)
2) any IDE can easily find the struct anyway

include/z64sram.h

@@ -0,0 +1,20 @@
+#ifndef Z64SRAM_H
+#define Z64SRAM_H
+
+#include "ultra64/ultratypes.h"
+
+typedef struct {
+    /* 0x00 */ u8* readBuff;
+} SramContext; // size = 0x4
+
+#define SRAM_SIZE 0x8000
+#define SRAM_HEADER_SIZE 0x10
+
+typedef enum {
+    /* 0x00 */ SRAM_HEADER_SOUND,
+    /* 0x01 */ SRAM_HEADER_ZTARGET,
+    /* 0x02 */ SRAM_HEADER_LANGUAGE,
+    /* 0x03 */ SRAM_HEADER_MAGIC // must be the value of `sZeldaMagic` for save to be considered valid
+} SramHeaderField;
+
+#endif