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/fatal/source/fatal_debug.cpp

@@ -156,7 +156,7 @@ namespace sts::fatal::srv {
 
     void TryCollectDebugInformation(ThrowContext *ctx, u64 process_id) {
         /* Try to debug the process. This may fail, if we called into ourself. */
-        AutoHandle debug_handle;
+        os::ManagedHandle debug_handle;
         if (R_FAILED(svcDebugActiveProcess(debug_handle.GetPointer(), process_id))) {
             return;
         }