hle: kernel: Refactor to allocate a ServiceThread per service handler.

- Previously, we would allocate a thread per session, which adds new threads on CloneCurrentObject.
- This results in race conditions with N sessions queuing requests to the same service interface.
- Fixes Pokken Tournament DX crashes/softlocks, which were regressed by #6347.

src/core/hle/kernel/hle_ipc.cpp

@@ -30,9 +30,16 @@
 
 namespace Kernel {
 
-SessionRequestHandler::SessionRequestHandler() = default;
+SessionRequestHandler::SessionRequestHandler(KernelCore& kernel_, const char* service_name_)
+    : kernel{kernel_}, service_thread{kernel.CreateServiceThread(service_name_)} {}
 
-SessionRequestHandler::~SessionRequestHandler() = default;
+SessionRequestHandler::~SessionRequestHandler() {
+    kernel.ReleaseServiceThread(service_thread);
+}
+
+SessionRequestManager::SessionRequestManager(KernelCore& kernel_) : kernel{kernel_} {}
+
+SessionRequestManager::~SessionRequestManager() {}
 
 void SessionRequestHandler::ClientConnected(KServerSession* session) {
     session->SetSessionHandler(shared_from_this());