bis_factory: Add partial implementation of BISFactory

Creates and stores RegisteredCaches for user and system NAND, as creation of a RegisteredCache is expensive.

src/core/file_sys/bis_factory.cpp

+// Copyright 2018 yuzu emulator team
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include "core/file_sys/bis_factory.h"
+
+namespace FileSys {
+
+BISFactory::BISFactory(VirtualDir nand_root_)
+    : nand_root(std::move(nand_root_)),
+      sysnand_cache(std::make_shared<RegisteredCache>(
+          nand_root->GetDirectoryRelative("/system/Contents/registered"))),
+      usrnand_cache(std::make_shared<RegisteredCache>(
+          nand_root->GetDirectoryRelative("/user/Contents/registered"))) {}
+
+std::shared_ptr<RegisteredCache> BISFactory::GetSystemNANDContents() const {
+    return sysnand_cache;
+}
+
+std::shared_ptr<RegisteredCache> BISFactory::GetUserNANDContents() const {
+    return usrnand_cache;
+}
+
+} // namespace FileSys

src/core/file_sys/bis_factory.h

+// Copyright 2018 yuzu emulator team
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <memory>
+#include "core/loader/loader.h"
+#include "registered_cache.h"
+
+namespace FileSys {
+
+/// File system interface to the Built-In Storage
+/// This is currently missing accessors to BIS partitions, but seemed like a good place for the NAND
+/// registered caches.
+class BISFactory {
+public:
+    explicit BISFactory(VirtualDir nand_root);
+
+    std::shared_ptr<RegisteredCache> GetSystemNANDContents() const;
+    std::shared_ptr<RegisteredCache> GetUserNANDContents() const;
+
+private:
+    VirtualDir nand_root;
+
+    std::shared_ptr<RegisteredCache> sysnand_cache;
+    std::shared_ptr<RegisteredCache> usrnand_cache;
+};
+
+} // namespace FileSys