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

[zjh]

On Thursday, 4 November 2021 at 02:26:20 UTC, Walter Bright wrote:
> https://issues.dlang.org/show_bug.cgi?id=22473
>

`string`, as a language part, should not be encoded at all. It is 
`(8-bit)` byte directly.
The standard library implement the required 'coding string'.
In this way, other people need various "coding strings", so they 
import the "coding strings" in the "standard library"
Just because the code is not 'utf8', and then you can't write 
`d`'s program, it's terrible.