feat: add comment-placer-component

[PedroMiguelSS]

This PR adds CommentPlacer component. The main goal of this component is to sync animations, scroll and automatic focus that may happen simultaneously.

It handles entry animations for comments. We have currently 2 different animations: FadeAndGrow and Fade. They are used in different cases: FadeAndGrow is applied whether a new comment or a reply textarea enters on the list.
Fade is used when an edit textarea appears.

Sync flows

• A comment enters the list -> FadeAndGrow entry animation occurs (if the comment will be visible) -> scroll to new comment (if I'm the author of the comment)
• Reply button clicked -> FadeAndGrow entry animation occurs (if the textarea will be visible) -> scroll to the element occurs -> automatic focus happens
• Edit button clicked -> Fade entry animation occurs to make textarea visible -> automatic focus happens
• Save button clicked on new reply -> focus is disabled -> Fade exiting animation occurs to unmount textarea and make the new comment visible.
• Cancel button clicked on new reply -> focus is disabled -> FadeAndGrow exiting animation occurs.
• Save button clicked on edit comment -> focus is disabled -> Fade exiting animation occurs to unmount textarea and make the old comment visible.
• Cancel button clicked on edit comment -> focus is disabled -> Fade exiting animation occurs to unmount textarea and make the edited comment visible.

This component also takes care of another animation: scale comments when they come into view (while users are scrolling the list). Kind of a skew effect.

Other components on this PR

• FadeAndGrowTransition
• FadeTransition
• FocusManager

[satazor]

I also think we are missing a README.md file and storybook entry for the CommentPlacer.

[satazor]

There's a bug in the textarea height animation in some situations but @acostalima will take care of it later on.