Fixes #83035.

• In native code we are checking if char is alphanumeric, if not we are replacing it with '_'. Unicode signs are treated as non-alphanumeric. To remain consistent, the same mechanism was added in the managed code, in FixupSymbolName.
• MSBuild task's logger changes unicode's chars:

  runtime/src/tasks/AotCompilerTask/MonoAOTCompiler.cs

  Line 984 in 004a2eb

  Log.LogMessage(MessageImportance.High, $"[{count}/{_totalNumAssemblies}] {Path.GetFileName(assembly)} -> {copiedFiles}");

  
  e.g. 煉 -> _┼í┼»├ź
  so that we cannot compare the build/publish output in the old way (using string contains). String comparison with the result that is displayed by the console (_┼í┼»├ź) is not effective either, so now we are checking for a regex.