BACKENDS: Add function in FS Factory to map scummvm path to system path

In most cases they are the same, but in the case of a sandboxed filesystem,
they may be different. Mapping to the full system path allows using the
path with system functions, such as fopen() or third party libraries (for
example to pass a soundfont path to the fluidsynth library).

backends/fs/chroot/chroot-fs-factory.cpp

@@ -74,4 +74,14 @@ void ChRootFilesystemFactory::addVirtualDrive(const Common::String &name, const
 	_virtualDrives[name] = path;
 }
 
+Common::String ChRootFilesystemFactory::getSystemFullPath(const Common::String& path) const {
+	size_t driveEnd = path.findFirstOf('/');
+	if (driveEnd != Common::String::npos && driveEnd > 0) {
+		auto it = _virtualDrives.find(path.substr(0, driveEnd));
+		if (it != _virtualDrives.end())
+			return it->_value + path.substr(driveEnd);
+	}
+	return _root + path;
+}
+
 #endif

backends/fs/chroot/chroot-fs-factory.h

@@ -40,6 +40,8 @@ public:
 	
 	void addVirtualDrive(const Common::String &name, const Common::String &path);
 
+	Common::String getSystemFullPath(const Common::String& path) const override;
+
 private:
 	const Common::String _root;
 	Common::StringMap _virtualDrives;

backends/fs/fs-factory.h

@@ -63,6 +63,15 @@ public:
 	 * On Windows, it will be a special node which "contains" all drives (C:, D:, E:).
 	 */
 	virtual AbstractFSNode *makeRootFileNode() const = 0;
+
+	/**
+	 * Returns a path suitable for systen functions such as fopen() for the given ScummVM path,
+	 *
+	 * In most cases the returned path is the same as the given path, but it may be different, for
+	 * example when the application is sandboxed and ScummVM path are relative to the saandbox
+	 * root.
+	 */
+	virtual Common::String getSystemFullPath(const Common::String& path) const { return path; }
 };
 
 #endif /*FILESYSTEM_FACTORY_H*/