Add option excludeEmptyString for regex validators and z.e164()

[evgeniyworkbel]

Yup has the option https://github.com/jquense/yup#stringmatchesregex-regex-options--message-string-excludeemptystring-bool--schema

I'm so waiting for this option in Zod because now custom validators looks confusable and not readable at all.
For example:
const latinTextOptionalValidator = z.string().regex(/^[A-Za-z]*/, "Text must contain latin letters").or(z.literal("")). This validator is hard to read, also I can't chain it with min() or max()
It's simple example, but in real development there are more complicated validators.

So it will be very nice if this option appears