Avoid unnecessary allocations in SanitizeEntryFilePath

On Windows, this method was allocating a StringBuilder, the underlying char[], and the resulting string, even if nothing needed to be changed.  We now only allocate anything if something needs to change, and if it does, we only allocate the string itself.

src/libraries/Common/src/System/IO/Archiving.Utils.Windows.cs

@@ -9,19 +9,38 @@ internal static partial class ArchivingUtils
     {
         internal static string SanitizeEntryFilePath(string entryPath)
         {
-            StringBuilder builder = new StringBuilder(entryPath);
+            // Find the first illegal character in the entry path.
             for (int i = 0; i < entryPath.Length; i++)
             {
-                if (((int)builder[i] >= 0 && (int)builder[i] < 32) ||
-                   builder[i] == '?' || builder[i] == ':' ||
-                   builder[i] == '*' || builder[i] == '"' ||
-                   builder[i] == '<' || builder[i] == '>' ||
-                   builder[i] == '|')
+                switch (entryPath[i])
                 {
-                    builder[i] = '_';
+                    // We found at least one character that needs to be replaced.
+                    case < (char)32 or '?' or ':' or '*' or '"' or '<' or '>' or '|':
+                        return string.Create(entryPath.Length, (i, entryPath), (dest, state) =>
+                        {
+                            string entryPath = state.entryPath;
+
+                            // Copy over to the new string everything until the character, then
+                            // substitute for the found character.
+                            entryPath.AsSpan(0, state.i).CopyTo(dest);
+                            dest[state.i] = '_';
+
+                            // Continue looking for and replacing any more illegal characters.
+                            for (int i = state.i + 1; i < entryPath.Length; i++)
+                            {
+                                char c = entryPath[i];
+                                dest[i] = c switch
+                                {
+                                    < (char)32 or '?' or ':' or '*' or '"' or '<' or '>' or '|' => '_',
+                                    _ => c,
+                                };
+                            }
+                        });
                 }
             }
-            return builder.ToString();
+
+            // There weren't any characters to sanitize.  Just return the original string.
+            return entryPath;
         }
     }
 }