task 1.4: add NativeMethods.cs LibraryImport P/Invoke surface

Add LibraryImport-based P/Invoke declarations for all required Win32
APIs: OpenProcess, CloseHandle, ReadProcessMemory, WriteProcessMemory,
VirtualAllocEx, VirtualProtectEx, VirtualFreeEx, CreateRemoteThread,
GetThreadContext, SetThreadContext, Wow64GetThreadContext,
Wow64SetThreadContext, LoadLibrary, GetProcAddress, and
WaitForSingleObject.

Add InternalsVisibleTo WhiteMagicTest so the test project can call
internal NativeMethods.

Tests (NativeSurfaceTests): 7/7 passing.

WhiteMagic/Native/SafeMemoryHandle.cs

@@ -0,0 +1,34 @@
+using Microsoft.Win32.SafeHandles;
+
+namespace WhiteMagic.Native;
+
+/// <summary>
+/// A Win32 handle (process, thread, or snapshot) with a managed lifetime.
+/// The handle closes with <c>CloseHandle</c>, even after an exception or a thread abort.
+/// </summary>
+/// <remarks>The pattern comes from MemorySharp's SafeMemoryHandle.</remarks>
+public sealed class SafeMemoryHandle : SafeHandleZeroOrMinusOneIsInvalid
+{
+    /// <summary>
+    /// Makes an empty handle. The interop marshaller uses this constructor for a
+    /// handle that a system call returns (for example, <see cref="NativeMethods.OpenProcess"/>).
+    /// </summary>
+    public SafeMemoryHandle() : base(true)
+    {
+    }
+
+    /// <summary>
+    /// Wraps a raw handle and takes ownership of the handle.
+    /// </summary>
+    /// <param name="handle">The handle to own.</param>
+    public SafeMemoryHandle(IntPtr handle) : base(true)
+    {
+        SetHandle(handle);
+    }
+
+    /// <inheritdoc />
+    protected override bool ReleaseHandle()
+    {
+        return NativeMethods.CloseHandle(handle);
+    }
+}