globset: support nested alternates

For example, `**/{node_modules/**/*/{ts,js},crates/**/*.{rs,toml}`.

I originally didn't add this I think for implementation simplicity, but
it turns out that it really isn't much work to do. There might have also
been some odd behavior in the regex engine for dealing with empty
alternates, but that has all been long fixed.

Closes #3048, Closes #3112

CHANGELOG.md

@@ -37,6 +37,8 @@ Feature enhancements:
   When using multithreading, schedule files to search in order given on CLI.
 * [FEATURE #2943](https://github.com/BurntSushi/ripgrep/issues/2943):
   Add `aarch64` release artifacts for Windows.
+* [FEATURE #3048](https://github.com/BurntSushi/ripgrep/pull/3048):
+  Globs in ripgrep (and the `globset` crate) now support nested alternates.
 
 
 14.1.1 (2024-09-08)