Last-chance exception handling could indicate how it was called

There are many codepaths that can get to [`DumpExceptionToFile`](https://github.com/rainersigwald/msbuild/blob/0a6e5f11fe3de4c5c9bf377b29b311507775e255/src/Shared/ExceptionHandling.cs#L280-L316), which is a last-ditch effort to try to preserve some debugging information in the case of bad failures. It'd be great if it was easy to identify _which path_ was used for a given exception dump. Knowing, for example, that this exception was caught by the `AppDomain`'s `UnhandledException` handler versus an explicit catch somewhere could be useful information.