Fix #17751 - q{} strings don't normalize CRLF to LF

[dkorpel]

Closes #17751

Apparently even single '\r' gets replaced by '\n' in string literals.

immutable char[] x = mixin("`a\r\b\r\nc\r\rd`");
pragma(msg, cast(ubyte[]) x);

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[dkorpel]

Still not using it because # is not valid in q{} strings (and a wysiwyg string is clearer here anyways)

[rikkimax]

This behavior of replacing \r with \n doesn't appear in the spec from what I can see, that should be noted.