bcat: Add backend function for BCAT Indirect (launch parameter)

Returns the data that should be returned by PopLaunchParameter kind=ApplicationSpecific.

src/core/hle/service/bcat/backend/backend.cpp

@@ -44,4 +44,10 @@ void NullBackend::SetPassphrase(u64 title_id, const Passphrase& passphrase) {
               Common::HexArrayToString(passphrase));
 }
 
+std::optional<std::vector<u8>> NullBackend::GetLaunchParameter(TitleIDVersion title) {
+    LOG_DEBUG(Service_BCAT, "called, title_id={:016X}, build_id={:016X}", title.title_id,
+              title.build_id);
+    return std::nullopt;
+}
+
 } // namespace Service::BCAT

src/core/hle/service/bcat/backend/backend.h

@@ -5,6 +5,7 @@
 #pragma once
 
 #include <functional>
+#include <optional>
 #include "common/common_types.h"
 #include "core/file_sys/vfs_types.h"
 
@@ -32,6 +33,8 @@ public:
 
     virtual void SetPassphrase(u64 title_id, const Passphrase& passphrase) = 0;
 
+    virtual std::optional<std::vector<u8>> GetLaunchParameter(TitleIDVersion title) = 0;
+
 protected:
     DirectoryGetter dir_getter;
 };
@@ -48,6 +51,8 @@ public:
     bool Clear(u64 title_id) override;
 
     void SetPassphrase(u64 title_id, const Passphrase& passphrase) override;
+
+    std::optional<std::vector<u8>> GetLaunchParameter(TitleIDVersion title) override;
 };
 
 std::unique_ptr<Backend> CreateBackendFromSettings(DirectoryGetter getter);