apt: Implement additional applet state management. (#6303)

* apt: Implement additional library applet state management.

* kernel: Clear process handle table on exit.

* apt: Implement system applet commands.

* apt: Pop MediaType from command buffers with correct size.

* apt: Improve accuracy of parameters and HLE applet lifecycle.

* apt: General cleanup.

* file_sys: Make system save data open error code more correct.

Not sure if this is the exact right error code, but it's at least
more correct than before as Game Notes will now create its system
save data instead of throwing a fatal error.

* apt: Fix launching New 3DS Internet Browser.

* frd: Correct fix to GetMyScreenName response.

src/core/hle/kernel/process.cpp

@@ -208,6 +208,9 @@ void Process::Exit() {
     if (plgldr) {
         plgldr->OnProcessExit(*this, kernel);
     }
+
+    // Clear the process's open handles.
+    handle_table.Clear();
 }
 
 VAddr Process::GetLinearHeapAreaAddress() const {