feat: Filter out unrepresentable schemas from unions

[Bram-dc]

I needed this to properly create openapi types for example my date schema:

export const zodISODateTime = () => {
	return z
		.union([z.date(), z.iso.datetime()])
		.overwrite((v) => {
			if (typeof v === 'string') {
				return new Date(v)
			}
			return v
		})
		.pipe(z.date())
}

z.date() is not representable, but I still want it to work internally. The resulting json schema should skip it.

I was thinking we should not create an extra unrepresentable option "filter" but instead include it in the "any" option, because this is also done for z.literal()

[Bram-dc]

I was thinking we should not create an extra unrepresentable option "filter" but instead include it in the "any" option, because this is also done for z.literal()

In this PR I did create an extra option. @colinhacks what are your thoughts?