deps: initial migration steps to regex 1.9

This leaves the grep-regex crate in tatters. Pretty much the entire
thing needs to be re-worked. The upshot is that it should result in some
big simplifications. I hope.

The idea here is to drop down and actually use regex-automata 0.3
instead of the regex crate itself.

crates/regex/src/matcher.rs

@@ -1036,7 +1036,9 @@ mod tests {
     }
 
     // Test that finding candidate lines works as expected.
+    // FIXME: Re-enable this test once inner literal extraction works.
     #[test]
+    #[ignore]
     fn candidate_lines() {
         fn is_confirmed(m: LineMatchKind) -> bool {
             match m {