FS.Archive: Clean up treatment of archives and their handles

- Refactor FS::Archive internals to make Archive creation and lifetime
  management clearer.
- Remove the "Archive as a File" hack.
- Implement 64-bit Archive handles.

src/core/file_sys/file_romfs.h

@@ -14,10 +14,11 @@
 
 namespace FileSys {
 
+class Archive_RomFS;
+
 class File_RomFS final : public FileBackend {
 public:
-    File_RomFS();
-    ~File_RomFS() override;
+    File_RomFS(const Archive_RomFS* archive) : archive(archive) {}
 
     /**
      * Open the file
@@ -62,6 +63,9 @@ public:
      * @return true if the file closed correctly
      */
     bool Close() const override;
+
+private:
+    const Archive_RomFS* archive;
 };
 
 } // namespace FileSys