os: implement waitable management.

This implements waitable management for Events (and
implements Events). It also refactors PM to use new
Event/Waitable semantics, and also adds STS_ASSERT
as a macro for asserting a boolean expression. The
rest of stratosphere has been refactored to use
STS_ASSERT whenever possible.

stratosphere/loader/source/ldr_loader_service.cpp

@@ -27,7 +27,7 @@ namespace sts::ldr {
 
     /* Official commands. */
     Result LoaderService::CreateProcess(Out<MovedHandle> proc_h, PinId id, u32 flags, CopiedHandle reslimit) {
-        AutoHandle reslimit_holder(reslimit.GetValue());
+        os::ManagedHandle reslimit_holder(reslimit.GetValue());
         ncm::TitleLocation loc;
         char path[FS_MAX_PATH];