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/boot/source/boot_calibration.cpp

@@ -38,9 +38,7 @@ namespace sts::boot {
                 0xA001, 0x6C00, 0x7800, 0xB401, 0x5000, 0x9C01, 0x8801, 0x4400
             };
 
-            if (data == nullptr) {
-                std::abort();
-            }
+            STS_ASSERT(data != nullptr);
 
             u16 crc16 = 0x55AA;
             const u8 *data_u8 = reinterpret_cast<const u8 *>(data);