service/am: Remove usages of global system accessors

Avoids the use of global accessors, removing the reliance on global
state. This also makes dependencies explicit in the interface, as
opposed to being hidden

src/core/core.cpp

@@ -104,7 +104,8 @@ FileSys::VirtualFile GetGameFileFromPath(const FileSys::VirtualFilesystem& vfs,
     return vfs->OpenFile(path, FileSys::Mode::Read);
 }
 struct System::Impl {
-    explicit Impl(System& system) : kernel{system}, cpu_core_manager{system}, reporter{system} {}
+    explicit Impl(System& system)
+        : kernel{system}, cpu_core_manager{system}, applet_manager{system}, reporter{system} {}
 
     Cpu& CurrentCpuCore() {
         return cpu_core_manager.GetCurrentCore();