[SelectField][TextField] Fix error styling issue

[oliviertassinari]

Fix #2532 and #2486.
Improved version of this PR #2534.

I have added some examples for the SelectField with the errorText property.
@subjectix I have also made the imperative setErrorText() and setValue() method deprecated.

[alitaheri]

@oliviertassinari This is good for now. patches up an ugly bug. but we'll need some major rewrite for these components. there are so many styling issues affecting them. For one, when the error appears it shouldn't take up more space, but rather reserve it's space (or some props should do that.). Implementing #2416 will make all our problems go away :D

[oliviertassinari]

@subjectix I have rebase to solve the conflict.

For one, when the error appears it shouldn't take up more space.

I'm not convinced by this, the errorText is not always here and can have an arbitrary height.

[alitaheri]

@oliviertassinari You have a point. But I've seen people having issues with this. when forms are prone to validation errors, some people would like to keep the spacing intact. I think we should implement the proposal in #2416 and add many options to for error text to support this use-case.

[alitaheri]

I'm merging this fix for now. Thanks @oliviertassinari
We have to discuss that further and it has nothing to do with this PR.

[pulse00]

Spacing of SelectFields with floating label is still an issues in 0.15 (see screenshot).
As soon as an item is selected an the floating label goes up, the text-field borders are aligned horizontally again.