Support custom legacy Sony devices with init.real setup

Custom ROM bring-ups of legacy Sony devices contain the following:
/init (symlink to /bin/init_sony)
/init.real (the "real" Android init)
/bin/init_sony (this was /sbin/init_sony on Android <11)

Kernel loads the ramdisk and starts /init -> /bin/init_sony
/bin/init_sony does low-level device setup (see: https://github.com/LineageOS/android_device_sony_common/blob/lineage-18.1/init/init_main.cpp)
/bin/init_sony unlinks /init and renames /init.real to /init
/bin/init_sony starts /init

Since init_sony needs to run first magiskinit needs to replace init.real instead, so add workarounds based on detection of init.real to boot patcher and uninstaller

Thanks @115ek and @bleckdeth

Fixes #3636

Co-authored-by: topjohnwu <topjohnwu@gmail.com>

native/jni/init/init.hpp

@@ -40,6 +40,7 @@ bool unxz(int fd, const uint8_t *buf, size_t size);
 void load_kernel_info(BootConfig *config);
 bool check_two_stage();
 void setup_klog();
+const char *backup_init();
 
 /***************
  * Base classes