[fixfon]

Fixes #15812

initial_quoting in shell_quoter.rs picks the quote character once. A name with ' and no other character from shell_escaped_char_set got double quotes, but ! is not in that set. An interactive bash expands ! inside double quotes, so ls on a file named x!#;touch PWNED;#' printed "x!#;touch PWNED;#'", and pasting that at a prompt runs the tail as a command. a'!b printed "a'!b", which fails with event not found. ! already counts as a special character in escaped_char.rs, but that only forces quoting; it never changes the quote kind.

I added ! to ESCAPED_CHARS, at the end because shell_escaped_char_set drops the first byte (:) for names that are not directories. A name with both ' and ! is now single-quoted with the apostrophe written as '\'', in all four shell styles and for printf %q and stat -c %N. Names with only ! or only ' print as before.

Tests: initial_quoting and test_special_chars_in_double_quotes in quoting_style, one ls test (file and -R heading) and one printf %q case. They fail on current main and pass with this change. cargo fmt, root cargo clippy --all-targets -- -D warnings, cargo test -p uucore quoting_style and the ls, printf and stat integration tests pass. Tested on macOS only.