Loader/NCCH: Add support for loading application updates (#2927)

* loader/ncch: split NCCH parsing into its own file

* loader/ncch: add support for loading update NCCHs from the SD card

* loader/ncch: fix formatting

* file_sys/ncch_container: Return a value for OpenFile

* loader/ncch: cleanup, always instantiate overlay_ncch to base_ncch

* file_sys/ncch_container: better encryption checks, allow non-app NCCHs to load properly and for the existence of NCCH structures to be checked

* file_sys/ncch_container: pass filepath as a const reference

src/core/loader/loader.h

@@ -166,6 +166,19 @@ public:
         return ResultStatus::ErrorNotImplemented;
     }
 
+    /**
+     * Get the update RomFS of the application
+     * Since the RomFS can be huge, we return a file reference instead of copying to a buffer
+     * @param romfs_file The file containing the RomFS
+     * @param offset The offset the romfs begins on
+     * @param size The size of the romfs
+     * @return ResultStatus result of function
+     */
+    virtual ResultStatus ReadUpdateRomFS(std::shared_ptr<FileUtil::IOFile>& romfs_file, u64& offset,
+                                         u64& size) {
+        return ResultStatus::ErrorNotImplemented;
+    }
+
     /**
      * Get the title of the application
      * @param title Reference to store the application title into