Refactor DSi_NAND (#1844)

* Refactor diskio's contents

- Change ff_disk_read_cb/write_cb into a std::function instead of a raw pointer
- Add const specifiers as needed

* Refactor DSi_NAND to manage the file system's mounted lifetime with RAII

* Split NANDMount into NANDMount and NANDImage

- NANDImage is used for information about the NAND that doesn't require decryption or filesystem access
- NANDMount is used to actually access the file system
- Both classes manage their respective resources (the NAND file handle and the NAND's mount) with RAII
- Also split the file loading into another function that I will remove in a later PR

* Make NANDMount immovable

* Remove NAND-loading code that I had sectioned off into a function

- Incomplete copypasta
- I must have gotten distracted

* Tidy up NANDImage's initialization

- Don't unmount the disk image if the constructor fails (that's NANDMount's job now)
- Only assign CurFile if the constructor succeeds

* Add some const-correctness

* Move DSi NAND initialization to the frontend

- The NANDImage is now installed via a unique_ptr in DSi

* Remove Platform::DSi_NANDPath

- Not Config::DSiNANDPath; that can still be configured as usual
- The core no longer needs to care

src/frontend/qt_sdl/TitleManagerDialog.h

@@ -19,6 +19,7 @@
 #ifndef TITLEMANAGERDIALOG_H
 #define TITLEMANAGERDIALOG_H
 
+#include <memory>
 #include <QDialog>
 #include <QMessageBox>
 #include <QListWidget>
@@ -30,6 +31,7 @@
 #include <QNetworkAccessManager>
 
 #include "DSi_TMD.h"
+#include "DSi_NAND.h"
 
 namespace Ui
 {
@@ -44,10 +46,10 @@ class TitleManagerDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit TitleManagerDialog(QWidget* parent);
+    explicit TitleManagerDialog(QWidget* parent, DSi_NAND::NANDImage& image);
     ~TitleManagerDialog();
 
-    static bool NANDInited;
+    static std::unique_ptr<DSi_NAND::NANDImage> nand;
     static bool openNAND();
     static void closeNAND();
 
@@ -68,7 +70,10 @@ public:
             return nullptr;
         }
 
-        currentDlg = new TitleManagerDialog(parent);
+        assert(nand != nullptr);
+        assert(*nand);
+
+        currentDlg = new TitleManagerDialog(parent, *nand);
         currentDlg->open();
         return currentDlg;
     }
@@ -89,6 +94,7 @@ private slots:
     void onExportTitleData();
 
 private:
+    DSi_NAND::NANDMount nandmount;
     Ui::TitleManagerDialog* ui;
 
     QString importAppPath;
@@ -106,7 +112,7 @@ class TitleImportDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit TitleImportDialog(QWidget* parent, QString& apppath, const DSi_TMD::TitleMetadata* tmd, bool& readonly);
+    explicit TitleImportDialog(QWidget* parent, QString& apppath, const DSi_TMD::TitleMetadata* tmd, bool& readonly, DSi_NAND::NANDMount& nand);
     ~TitleImportDialog();
 
 private slots:
@@ -119,6 +125,7 @@ private slots:
 
 private:
     Ui::TitleImportDialog* ui;
+    DSi_NAND::NANDMount& nandmount;
 
     QButtonGroup* grpTmdSource;