Simplify encoding detection using SourceText auto-detection

- Remove custom DetectEncoding() method and use SourceText.From(stream, encoding: null)
- SourceText automatically detects encoding including BOM when encoding is null
- Move <see href/> tags inside <summary> elements for better documentation
- Simplifies implementation while maintaining full functionality

Co-authored-by: jjonescz <[email protected]>

src/Cli/Microsoft.DotNet.FileBasedPrograms/FileLevelDirectiveHelpers.cs

@@ -258,30 +258,8 @@ internal readonly record struct SourceFile(string Path, SourceText Text)
     public static SourceFile Load(string filePath)
     {
         using var stream = File.OpenRead(filePath);
-        // Detect BOM to determine the appropriate encoding
-        Encoding encoding = DetectEncoding(stream);
-        stream.Position = 0; // Reset stream position after BOM detection
-        return new SourceFile(filePath, SourceText.From(stream, encoding));
-    }
-
-    private static Encoding DetectEncoding(Stream stream)
-    {
-        // UTF-8 BOM is 0xEF 0xBB 0xBF
-        if (stream.Length < 3)
-        {
-            return new UTF8Encoding(encoderShouldEmitUTF8Identifier: false);
-        }
-
-#if NETCOREAPP
-        Span<byte> buffer = stackalloc byte[3];
-        int bytesRead = stream.Read(buffer);
-#else
-        byte[] buffer = new byte[3];
-        int bytesRead = stream.Read(buffer, 0, 3);
-#endif
-        bool hasUtf8Bom = bytesRead == 3 && buffer[0] == 0xEF && buffer[1] == 0xBB && buffer[2] == 0xBF;
-
-        return new UTF8Encoding(encoderShouldEmitUTF8Identifier: hasUtf8Bom);
+        // Let SourceText.From auto-detect the encoding (including BOM detection)
+        return new SourceFile(filePath, SourceText.From(stream, encoding: null));
     }
 
     public SourceFile WithText(SourceText newText)

test/dotnet.Tests/CommandTests/Run/FileBasedAppSourceEditorTests.cs

@@ -520,8 +520,8 @@ public void RemoveMultiple()
     /// <summary>
     /// Verifies that files without UTF-8 BOM don't get one added when saved.
     /// This is critical for shebang (#!) scripts on Unix-like systems.
-    /// </summary>
     /// <see href="https://github.com/dotnet/sdk/issues/52054"/>
+    /// </summary>
     [Fact]
     public void PreservesNoBomEncoding()
     {
@@ -550,8 +550,8 @@ public void PreservesNoBomEncoding()
 
     /// <summary>
     /// Verifies that files with UTF-8 BOM preserve it when saved.
-    /// </summary>
     /// <see href="https://github.com/dotnet/sdk/issues/52054"/>
+    /// </summary>
     [Fact]
     public void PreservesBomEncoding()
     {