mem: implement most of StandardAllocator (#860)

This was tested using `https://github.com/node-dot-cpp/alloc-test` plus a few other by-hand tests.

It seems to work for the case we care about (sysmodules without thread cache-ing).

External users are advised to build with assertions on and contact SciresM if you find issues.

This is a lot of code to have gotten right in one go, and it was written mostly after midnight while sick, so there are probably un-noticed issues.

libraries/libstratosphere/include/stratosphere/os/os_thread.hpp

@@ -101,10 +101,19 @@ namespace ams::os {
             }
     };
 
-    NX_INLINE u32 GetCurrentThreadPriority() {
-        u32 prio;
+    ALWAYS_INLINE s32 GetCurrentThreadPriority() {
+        s32 prio;
         R_ABORT_UNLESS(svcGetThreadPriority(&prio, CUR_THREAD_HANDLE));
         return prio;
     }
 
+    /* TODO: ThreadManager? */
+    ALWAYS_INLINE s32 GetCurrentProcessorNumber() {
+        return svcGetCurrentProcessorNumber();
+    }
+
+    ALWAYS_INLINE s32 GetCurrentCoreNumber() {
+        return GetCurrentProcessorNumber();
+    }
+
 }