ams: mark ams::Result [[nodiscard]] (partially complete).

NOTE: This work is not yet fully complete; kernel is done, but
it was taking an exceedingly long time to get through libstratosphere.
Thus, I've temporarily added -Wno-error=unused-result for libstratosphere/stratosphere.

All warnings should be fixed to do the same thing Nintendo does as relevant, but this
is taking a phenomenally long time and is not actually the most important work to do,
so it can be put off for some time to prioritize other tasks for 21.0.0 support.

libraries/libmesosphere/source/kern_k_system_resource.cpp

@@ -42,7 +42,7 @@ namespace ams::kern {
         R_UNLESS(m_resource_size > rc_size, svc::ResultOutOfMemory());
 
         /* Initialize slab heaps. */
-        m_dynamic_page_manager.Initialize(m_resource_address + rc_size, m_resource_size - rc_size, PageSize);
+        R_TRY(m_dynamic_page_manager.Initialize(m_resource_address + rc_size, m_resource_size - rc_size, PageSize));
         m_page_table_heap.Initialize(std::addressof(m_dynamic_page_manager), 0, GetPointer<KPageTableManager::RefCount>(m_resource_address));
         m_memory_block_heap.Initialize(std::addressof(m_dynamic_page_manager), 0);
         m_block_info_heap.Initialize(std::addressof(m_dynamic_page_manager), 0);