Infinite loop in `Pattern#compile` on certain case-insensitive patterns

`Pattern.compile("(?i)ᲀ")` hangs in an infinite loop with JDK 11 and 17, but not 8. Other characters from the Cyrillic Extended-C block trigger the same behavior.

Stack trace captured with `jcmd`:
```
at java.lang.Character.toLowerCase(java.base@19.0.2/Character.java:10710)
at com.google.re2j.Characters.toLowerCase(Characters.java:14)
at com.google.re2j.Unicode.simpleFold(Unicode.java:118)
at com.google.re2j.Parser.minFoldRune(Parser.java:200)
at com.google.re2j.Parser.newLiteral(Parser.java:187)
at com.google.re2j.Parser.literal(Parser.java:211)
at com.google.re2j.Parser.parseInternal(Parser.java:807)
at com.google.re2j.Parser.parse(Parser.java:790)
at com.google.re2j.RE2.compileImpl(RE2.java:185)
at com.google.re2j.Pattern.compile(Pattern.java:151)
at com.google.re2j.Pattern.compile(Pattern.java:109)
```

I first submitted this as a security issue since I understood the README to indicate that re2j should be considered safe to use on untrusted regexes of bounded length, but was told that this is *not* the case and that there are many known ways to "crash" re2j with crafted regular expressions.

I would thus welcome a clear statement on the security guarantees provided by re2j in the README.

Edit: Looks like https://groups.google.com/g/re2j-discuss/c/9XkVsnxngjc could resolve this issue.