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_getter_impl.hpp

@@ -0,0 +1,44 @@
+/*
+ * 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>
+#include "lm_custom_sink_buffer.hpp"
+
+namespace ams::lm::srv {
+
+    class LogGetterImpl {
+        NON_COPYABLE(LogGetterImpl);
+        NON_MOVEABLE(LogGetterImpl);
+        private:
+            static constinit inline const u8 *s_message = nullptr;
+            static constinit inline size_t s_buffer_size = 0;
+            static constinit inline size_t s_log_packet_drop_count = 0;
+        private:
+            LogGetterImpl();
+        public:
+            static CustomSinkBuffer &GetBuffer();
+            static s64 GetLog(void *buffer, size_t buffer_size, u32 *out_drop_count);
+
+            static void IncreaseLogPacketDropCount() { ++s_log_packet_drop_count; }
+        private:
+            static bool FlushFunction(const u8 *buffer, size_t buffer_size) {
+                s_message     = buffer;
+                s_buffer_size = buffer_size;
+                return true;
+            }
+    };
+
+}