Codechange: Pass span to StrValid instead of first and last - 1. (#12846)

`std::span` is used instead of `std::string_view` as this is only used for fixed-length buffers.

This removes some callers of `lastof()`

src/string_func.h

@@ -27,7 +27,7 @@ void StrMakeValidInPlace(char *str, StringValidationSettings settings = SVS_REPL
 
 bool strtolower(std::string &str, std::string::size_type offs = 0);
 
-[[nodiscard]] bool StrValid(const char *str, const char *last) NOACCESS(2);
+[[nodiscard]] bool StrValid(std::span<const char> str);
 void StrTrimInPlace(std::string &str);
 std::string_view StrTrimView(std::string_view str);