Add GIF select to composer (#3600)

* create dialog with flatlist in it

* use alf for composer photos/camera/gif buttons

* add gif icons

* focus textinput on gif dialog close

* add giphy API + gif grid

* web support

* add consent confirmation

* track gif select

* desktop web consent styles

* use InlineLinkText instead of Link

* add error/loading state

* hide sideborders on web

* disable composer buttons where necessary

* skip cardyb and set thumbnail directly

* switch legacy analytics to statsig

* remove autoplay prop

* disable photo/gif buttons if external media is present

* memoize listmaybeplaceholder

* fix pagination

* don't set `value` of TextInput, clear via ref

* remove console.log

* close modal if press escape

* pass alt text in the description

* Fix typo

* Rm dialog

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Co-authored-by: Dan Abramov <dan.abramov@gmail.com>

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