interp: add dotglob support

[aucampia]

Bash supports dotglob, but as far as I can tell mvdan.cc/sh/v3/cmd/gosh does not:

$ go run mvdan.cc/sh/v3/cmd/gosh@latest -c 'shopt -s globstar; shopt -s dotglob; printf "%s\n" ./**/README*'
shopt: invalid option name "dotglob" "off" ("on" not supported)

Just want to know if you are open to including support for it.

[mvdan]

Yes of course - within reason, any useful Bash feature should be added to the interpreter.