Avoid calling GetTempFileName in BitmapDownload

Replace the Win32 GetTempFileName P/Invoke with Path.GetTempFileName,
whose .NET 8+ implementation avoids the 65k file limit by generating
random filenames internally.

Fixes #259

Author: apoorvdarshan

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Imaging/BitmapDownload.cs

@@ -9,7 +9,6 @@
 using MS.Internal;
 using System.Net;
 using System.Net.Cache;
-using System.Text;
 using MS.Win32;
 using Microsoft.Win32.SafeHandles;
 
@@ -111,16 +110,14 @@ Stream stream
             entry.inputUri = uri;
             entry.inputStream = stream;
 
-            string cacheFolder = MS.Win32.WinInet.InternetCacheFolder.LocalPath;
             bool passed = false;
 
-            // Get the file path 
-            StringBuilder tmpFileName = new StringBuilder(NativeMethods.MAX_PATH);
-            MS.Win32.UnsafeNativeMethods.GetTempFileName(cacheFolder, "WPF", 0, tmpFileName);
-              
+            // Use Path.GetTempFileName whose .NET 8+ implementation avoids the
+            // Win32 GetTempFileName 65k file limit by generating random filenames.
+            string pathToUse = Path.GetTempFileName();
+
             try
             {
-                string pathToUse = tmpFileName.ToString();
                 SafeFileHandle fileHandle = MS.Win32.UnsafeNativeMethods.CreateFile(
                     pathToUse,
                     dwDesiredAccess: NativeMethods.GENERIC_READ | NativeMethods.GENERIC_WRITE,
@@ -135,7 +132,7 @@ Stream stream
                 {
                     throw new Win32Exception();
                 }
-                    
+
                 entry.outputStream = new FileStream(fileHandle, FileAccess.ReadWrite);
                 entry.streamPath = pathToUse;
                 passed = true;

src/Microsoft.DotNet.Wpf/src/Shared/MS/Win32/UnsafeNativeMethodsOther.cs

@@ -14,20 +14,6 @@ namespace MS.Win32
 {
     internal partial class UnsafeNativeMethods
     {
-        [DllImport(ExternDll.Kernel32, CharSet = CharSet.Unicode, SetLastError = true, EntryPoint = "GetTempFileName")]
-        internal static extern uint _GetTempFileName(string tmpPath, string prefix, uint uniqueIdOrZero, StringBuilder tmpFileName);
-
-        internal static uint GetTempFileName(string tmpPath, string prefix, uint uniqueIdOrZero, StringBuilder tmpFileName)
-        {
-            uint result = _GetTempFileName(tmpPath, prefix, uniqueIdOrZero, tmpFileName);
-            if (result == 0)
-            {
-                throw new Win32Exception();
-            }
-
-            return result;
-        }
-
         [DllImport(ExternDll.Shell32, CharSet = CharSet.Auto, BestFitMapping = false, ThrowOnUnmappableChar = true)]
         internal static extern int ExtractIconEx(
                                         string szExeFileName,