Server side validation for property editors (multiple text strings and block list)

[AndyButland]

Prerequisites

• I have added steps to test this contribution in the description below

Description

This adds server-side validation to the multiple text strings, to ensure that the number of entries provided matches the configured minimum and maximum.

For the block list, the validation was already in place, so here all I've done is add unit tests.

As well as the unit tests, to verify manually I've used Swagger and manipulated values to the PUT /umbraco/management/api/v1.1/document/{id}/validate endpoint. You should find if you supply collection of strings or blocks above or below the configured range, you'll get a localized validation message in response.

[nikolajlauridsen]

Looks good 👍

I found one minor thing, if no max configuration was provided for the multiple text strings was provided you weren't allowed to publish any multiple text strings because the max configuration defaults to 0 because it's not nullabe, I've added a test showing this and fixed the issue 👍

Feel free to merge if you're happy with my changes :D

[AndyButland]

Thanks @nikolajlauridsen, and good catch on the max configuration.