Support nested + lowercase components

[bpierre]

This is to support the Animated library used by react-spring with the css prop.

Pseudocode to illustrate:

// in
<animated.div css="color: red" />

// out (before the change)
styled("animated.div")`
  color: red
`

// out (after the change)
styled(animated.div)`
  color: red
`

[bpierre]

Is there anything I can do to make this easier to review?

[quantizor]

I'm going to merge your PR into mine as it has some other css prop changes and the fixtures are going to have further merge conflicts

[quantizor]

Cherry-picked over to #228 with authorship retained, thanks!