dmd foreach loops throw exceptions on invalid UTF sequences, use replacementDchar instead

[Adam D Ruppe]

On Thursday, 4 November 2021 at 02:26:20 UTC, Walter Bright wrote:
> I've tried to fix this before, but too many people objected.

I proposed a few days ago that Phobos autodecoding, if not 
completely removed, do this exact same thing too.

I agree it is a good idea. If you want an exception, it is easy 
enough to just check it in the loop and throw then.

Let's do it.