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_custom_sink_buffer.cpp

@@ -0,0 +1,60 @@
+/*
+ * 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/>.
+ */
+#include <stratosphere.hpp>
+#include "lm_custom_sink_buffer.hpp"
+
+namespace ams::lm::srv {
+
+    bool CustomSinkBuffer::TryPush(const void *data, size_t size) {
+        /* Check pre-conditions. */
+        AMS_ASSERT(size <= m_buffer_size);
+        AMS_ASSERT(data || size == 0);
+
+        /* If we have nothing to push, succeed. */
+        if (size == 0) {
+            return true;
+        }
+
+        /* Check that we can push the data. */
+        if (size > m_buffer_size - m_used_buffer_size) {
+            return false;
+        }
+
+        /* Push the data. */
+        std::memcpy(m_buffer + m_used_buffer_size, data, size);
+        m_used_buffer_size += size;
+
+        return true;
+    }
+
+    bool CustomSinkBuffer::TryFlush() {
+        /* Check that we have data to flush. */
+        if (m_used_buffer_size == 0) {
+            return false;
+        }
+
+        /* Try to flush the data. */
+        if (!m_flush_function(m_buffer, m_used_buffer_size)) {
+            return false;
+        }
+
+        /* Clear our used size. */
+        m_used_buffer_size = 0;
+
+        return true;
+    }
+
+}