feat(translate): add translation presets and custom instructions

src/translate/translationservice.h

@@ -8,6 +8,7 @@
 #include <QObject>
 #include <QStringList>
 #include <QUrl>
+#include <QVariantList>
 #include <QVariantMap>
 #include <QtQml/qqmlregistration.h>
 
@@ -28,6 +29,7 @@ class TranslationService : public QObject
     Q_PROPERTY(QString statusText READ statusText NOTIFY statusTextChanged)
     Q_PROPERTY(QString errorText READ errorText NOTIFY errorTextChanged)
     Q_PROPERTY(QStringList availableModels READ availableModels NOTIFY availableModelsChanged)
+    Q_PROPERTY(QVariantList translationPresets READ translationPresets CONSTANT)
     Q_PROPERTY(bool fetchingModels READ isFetchingModels NOTIFY fetchingModelsChanged)
 
 public:
@@ -39,6 +41,7 @@ public:
     QString statusText() const;
     QString errorText() const;
     QStringList availableModels() const;
+    QVariantList translationPresets() const;
     bool isFetchingModels() const;
 
     // \a track is an entry of MpvItem::subtitleTracks.