Boss Rush cleanup (#5652)

* Reduce stuff in the `.h`s & use `COND_HOOK` + variants

* Move some boss rush stuff from `z_file_choose.c`

* clang

* Update BossRush.cpp

soh/include/z64.h

@@ -1522,7 +1522,7 @@ typedef struct {
     /* 0x34 */ s32 isEnabled;
 } StickDirectionPrompt;
 
-typedef struct {
+typedef struct FileChooseContext {
     /* 0x00000 */ GameState state;
     /* 0x000A4 */ Vtx* windowVtx;
     /* 0x000A8 */ u8* staticSegment;