note to maintainers: should be merged in 2.3

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I'd like to note that many built-in form types are also prone to this behaviour:

• BirthdayType has 'years' parameter that's supposed to be an array that gets passed to DateType;
• ChoiceType expects 'preferred_choices' to be an array as this option is then passed to SimpleChoiceList constructor without any checks, and before setAllowedTypes is called;
• CollectionType expects 'options' to be an array as options are then passed to $optionsNormalizer which uses string keys
• CountryType, LanguageType, LocaleType, TimezoneType and CurrencyType could behave strange when a string is passed as 'choices' value; no checks here, too;
• DateType::listMonths, listYears and listDays all expect an array (it's typehinted) though the allowed type is not set
• TimeType has lots of logic that could possibly misbehave due to 'hours', 'minutes', 'seconds'
• TimeTypecould possibly misbehave due to 'emptyValue' option, though there are some dependencies there.
• UrlType can behave strange when a 'default_protocol' option is not an array.

Could fixing these types improve [DX]?

@kix Thanks for your investigation! Do you want to add fixes for these other problems to this PR?

@webmozart, sure, I've been doing some testing; currently thinking of a correct way to implement this all (some types are not so easy to figure out, like the Date)

@kix A good approach is to start with the trivial fixes first, and keep the more complicated ones for a later PR where we discuss some more.

@webmozart, sure, basically that's what I intended to do :)

Actually, the problem in ChoiceType and its derivatives is caused by OptionsResolver\OptionsResolver and OptionsResolver\Options.
The Options::all() call in OptionsResolver::resolve() leads to normalization being called, and this happens before options validation, which causes our problems.
Hence, any FormType that needs normalized options is not guaranteed to have valid options passed to the normalizers.

ChoiceType, CollectionType, CountryType, LanguageType, LocaleType, TimezoneType, TimeType and CurrencyType depend on normalizer logic implemented in OptionsResolver\Options.
Basically, this pull request is complete, and a new issue needs to be created on OptionsResolver::resolve() and Options::all() behaviour.

OptionsResolver problem is described in #4500, fixing it should open the way for some more form type fixes.

Thank you so much Stepan! This is merged into 2.3 now. #4500 is being fixed in #12156, do you want to work on the remaining types after that?

@webmozart, well, if it's merged then why not? I'll make another PR then.