WebformEmailMultiple validation too strict when using tokens

When defining an email handler email address, webform uses the #allow_tokens option. In this case, it skips the regular email validator if the value starts and ends with a token /^\[.*\]$/. There are many valid email address that can be made up from tokens that don't match this pattern, such as [member-name]@[domain] or [member-name]@domain.com or even "[name]" <[mail]>.

I suggest we relax the pattern to just test to see if a token is present, not that it is the whole string.