Remove a few more instances of unsafe code in STJ

src/libraries/Common/src/System/HexConverter.cs

@@ -178,7 +178,7 @@ public static void EncodeToUtf16(ReadOnlySpan<byte> bytes, Span<char> chars, Cas
             }
         }
 
-        public static unsafe string ToString(ReadOnlySpan<byte> bytes, Casing casing = Casing.Upper)
+        public static string ToString(ReadOnlySpan<byte> bytes, Casing casing = Casing.Upper)
         {
 #if NETFRAMEWORK || NETSTANDARD2_0
             Span<char> result = bytes.Length > 16 ?
@@ -192,12 +192,26 @@ public static unsafe string ToString(ReadOnlySpan<byte> bytes, Casing casing = C
                 pos += 2;
             }
             return result.ToString();
+#elif NET9_0_OR_GREATER
+            SpanCasingPair args = new() { Bytes = bytes, Casing = casing };
+            return string.Create(bytes.Length * 2, args, static (chars, args) =>
+                EncodeToUtf16(args.Bytes, chars, args.Casing));
 #else
-            return string.Create(bytes.Length * 2, (RosPtr: (IntPtr)(&bytes), casing), static (chars, args) =>
-                EncodeToUtf16(*(ReadOnlySpan<byte>*)args.RosPtr, chars, args.casing));
+            // .NET 8.0 path (doesn't support 'allow ref struct' feature)
+            unsafe
+            {
+                return string.Create(bytes.Length * 2, (RosPtr: (IntPtr)(&bytes), casing), static (chars, args) =>
+                    EncodeToUtf16(*(ReadOnlySpan<byte>*)args.RosPtr, chars, args.casing));
+            }
 #endif
         }
 
+        private ref struct SpanCasingPair
+        {
+            public ReadOnlySpan<byte> Bytes { get; set; }
+            public Casing Casing { get; set; }
+        }
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static char ToCharUpper(int value)
         {

src/libraries/Common/src/System/Text/ValueStringBuilder.cs

@@ -235,22 +235,6 @@ public void Append(char c, int count)
             _pos += count;
         }
 
-        public unsafe void Append(char* value, int length)
-        {
-            int pos = _pos;
-            if (pos > _chars.Length - length)
-            {
-                Grow(length);
-            }
-
-            Span<char> dst = _chars.Slice(_pos, length);
-            for (int i = 0; i < dst.Length; i++)
-            {
-                dst[i] = *value++;
-            }
-            _pos += length;
-        }
-
         public void Append(scoped ReadOnlySpan<char> value)
         {
             int pos = _pos;

src/libraries/Common/tests/Tests/System/Text/ValueStringBuilderTests.cs

@@ -103,25 +103,6 @@ public void Append_CharInt_MatchesStringBuilder()
             Assert.Equal(sb.ToString(), vsb.ToString());
         }
 
-        [Fact]
-        public unsafe void Append_PtrInt_MatchesStringBuilder()
-        {
-            var sb = new StringBuilder();
-            var vsb = new ValueStringBuilder();
-            for (int i = 1; i <= 100; i++)
-            {
-                string s = i.ToString();
-                fixed (char* p = s)
-                {
-                    sb.Append(p, s.Length);
-                    vsb.Append(p, s.Length);
-                }
-            }
-
-            Assert.Equal(sb.Length, vsb.Length);
-            Assert.Equal(sb.ToString(), vsb.ToString());
-        }
-
         [Fact]
         public void AppendSpan_DataAppendedCorrectly()
         {
@@ -266,7 +247,7 @@ public void Dispose_ClearsBuilder_ThenReusable()
         }
 
         [Fact]
-        public unsafe void Indexer()
+        public void Indexer()
         {
             const string Text1 = "foobar";
             var vsb = new ValueStringBuilder();

src/libraries/System.Private.Uri/src/System/PercentEncodingHelper.cs

@@ -93,7 +93,7 @@ public static unsafe int UnescapePercentEncodedUTF8Sequence(char* input, int len
                 {
                     if (charsToCopy != 0)
                     {
-                        dest.Append(input + totalCharsConsumed - charsToCopy, charsToCopy);
+                        dest.Append(new ReadOnlySpan<char>(input + totalCharsConsumed - charsToCopy, charsToCopy));
                         charsToCopy = 0;
                     }
 
@@ -167,7 +167,7 @@ public static unsafe int UnescapePercentEncodedUTF8Sequence(char* input, int len
                 return totalCharsConsumed;
 
             bytesLeftInBuffer *= 3;
-            dest.Append(input + totalCharsConsumed - charsToCopy, charsToCopy + bytesLeftInBuffer);
+            dest.Append(new ReadOnlySpan<char>(input + totalCharsConsumed - charsToCopy, charsToCopy + bytesLeftInBuffer));
             return totalCharsConsumed + bytesLeftInBuffer;
         }
     }

src/libraries/System.Private.Uri/src/System/UriHelper.cs

@@ -365,7 +365,7 @@ internal static unsafe void UnescapeString(char* pStr, int start, int end, ref V
         {
             if ((unescapeMode & UnescapeMode.EscapeUnescape) == UnescapeMode.CopyOnly)
             {
-                dest.Append(pStr + start, end - start);
+                dest.Append(new ReadOnlySpan<char>(pStr + start, end - start));
                 return;
             }