- WritableRegion: enable wrapping IMemoryOwner<byte>

- IVirtualMemoryManager impls of GetWritableRegion() use pooled memory when region is non-contiguous.
- IVirtualMemoryManager: add GetReadOnlySequence() and impls
- ByteMemoryPool: add new method RentCopy()
- ByteMemoryPool: make class static, remove ctor and singleton field from earlier impl

src/Ryujinx.Common/Memory/BytesReadOnlySequenceSegment.cs

@@ -0,0 +1,26 @@
+using System;
+using System.Buffers;
+
+namespace Ryujinx.Common.Memory
+{
+    /// <summary>
+    /// A concrete implementation of <seealso cref="ReadOnlySequence{T}"/>,
+    /// with methods to help build a full sequence.
+    /// </summary>
+    public sealed class BytesReadOnlySequenceSegment : ReadOnlySequenceSegment<byte>
+    {
+        public BytesReadOnlySequenceSegment(Memory<byte> memory) => Memory = memory;
+
+        public BytesReadOnlySequenceSegment Append(Memory<byte> memory)
+        {
+            var nextSegment = new BytesReadOnlySequenceSegment(memory)
+            {
+                RunningIndex = RunningIndex + Memory.Length
+            };
+
+            Next = nextSegment;
+
+            return nextSegment;
+        }
+    }
+}