Simplify Composer buttons (#7678)
* Render a CollapsibleButton's children (needed by UploadButton)
* Make UploadButton ready to live inside an overflow menu
* Always show overflow menu in composer: main buttons are emoji and attach
* Re-order composer buttons as per design
* Re-word composer button captions to be simple nouns
* Don't rotate More options button when clicked
* Move the composer menu and dialogs 16px in from right
* Reduce shadow on composer More menu
* From review: remove else clause
* From review: take input out of button
* Update test snapshots
* Update snapshots
