feat(TextArea): add component

[lucivpav]

Implements #755

Prop	Meaning
accessibility?	Accessibility behavior if overridden by the user.
defaultValue?	The default value of the text area.
onChange?	Called on change.
value?	The value of the text area.
disabled?	The text area becomes read-only.

Semantic UI's TextArea for reference
Mozilla's docs on <textarea>

[lucivpav]

There is a problem (along the lines: "A component is changing an uncontrolled input of type text to be controlled error in ReactJS") when one plays with placeholder in the playground. So I decided to disable it.

[layershifter]

Can be reenabled now?

[lucivpav]

Since there is no longer placeholder prop on (nor maxLength prop), it can be enabled. But I am not sure about its value

[layershifter]

Let's add a common test

[miroslavstastny]

Are there any props you would change/add? Such as minHeight??

No minHeight we have design prop for that. Once you set correct className on ElementType this will work: <TextArea design={{minHeight: '400px'}} />

[lucivpav]

Let's add a common test

I added unit test as well as a behavior test

[lucivpav]

There should be a text text to the textarea that has limited number of characters. (And used aria-describedby/labeledby)

[layershifter]

Left minor comments, LGTM 👍

Let's add some dumb styles and variables (for margin: 0, resize: vertical) to create boilerplate under Teams theme. And add an entry to CHANGELOG.md before merging 😼