Improve ValuePicker doc

[glebfox]

Existing page: https://docs.jmix.io/jmix/flow-ui/vc/components/valuePicker.html

1. Improve Basics section. Currently it has the following component definition:

valuePicker can have a label and both custom and predefined actions:

First, it seems that mention label is redundant, because it's a common attribute. Second, actions are described in the next section.

Probably, just show an example of basic usage without a phrase above.

3. Add css, ariaLabel, ariaLabelBy, focusShortcut common attributes
4. Remove requiredIndicatorVisible, invalid
5. Add missing elements: prefix, suffix