Misc performance tweaks (#4509)

* use Array.Empty() where instead of allocating new zero-length arrays

* structure for loops in a way that the JIT will elide array/Span bounds checking

* avoiding function calls in for loop condition tests

* avoid LINQ in a hot path

* conform with code style

* fix mistake in GetNextWaitingObject()

* fix GetNextWaitingObject() possibility of returning null if all list items have TimePoint == long.MaxValue

* make GetNextWaitingObject() behave FIFO behavior for multiple items with the same TimePoint

Ryujinx.Memory.Tests/MockVirtualMemoryManager.cs

@@ -78,7 +78,7 @@ namespace Ryujinx.Memory.Tests
 
         IEnumerable<MemoryRange> IVirtualMemoryManager.GetPhysicalRegions(ulong va, ulong size)
         {
-            return NoMappings ? new MemoryRange[0] : new MemoryRange[] { new MemoryRange(va, size) };
+            return NoMappings ? Array.Empty<MemoryRange>() : new MemoryRange[] { new MemoryRange(va, size) };
         }
 
         public bool IsMapped(ulong va)