LogManager: implement system module, client api, logging api (#1617)

Some notes:

* Unless `atmosphere!enable_log_manager` is true, Nintendo's log manager will be used instead.
  * This prevents paying memory costs for LM when not enabling logging.
  * To facilitate this, Atmosphere's log manager has a different program id from Nintendo's.
  * `atmosphere!enable_htc` implies `atmosphere!enable_log_manager`.
* LogManager logs to tma, and the SD card (if `lm!enable_sd_card_logging` is true, which it is by default).
* Binary logs are saved to `lm!sd_card_log_output_directory`, which is `atmosphere/binlogs` by default.

libraries/libstratosphere/source/lm/srv/lm_log_server_proxy.hpp

@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+#include <stratosphere.hpp>
+
+namespace ams::lm::srv {
+
+    class LogServerProxy {
+        AMS_SINGLETON_TRAITS(LogServerProxy);
+        public:
+            using ConnectionObserver = void (*)(bool connected);
+        private:
+            alignas(os::ThreadStackAlignment) u8 m_thread_stack[4_KB];
+            os::ThreadType m_thread;
+            os::SdkConditionVariable m_cv_connected;
+            os::Event m_stop_event;
+            os::SdkMutex m_connection_mutex;
+            os::SdkMutex m_observer_mutex;
+            std::atomic<int> m_server_socket;
+            std::atomic<int> m_client_socket;
+            ConnectionObserver m_connection_observer;
+        public:
+            void Start();
+            void Stop();
+
+            bool IsConnected();
+
+            void SetConnectionObserver(ConnectionObserver observer);
+
+            bool Send(const u8 *data, size_t size);
+        private:
+            void LoopAuto();
+            void SignalConnection();
+            void InvokeConnectionObserver(bool connected);
+    };
+
+    void StartLogServerProxy();
+    void StopLogServerProxy();
+
+}