Investigate more usages of transitions and animations to remove for users with `prefer-reduced-motion`

We've removed some animations in #3972. But we do have some more transitions as Julien wrote in his review message. We should investigate them and remove them for users with `prefer-reduced-motion` if they are a problem for them.

Here's the list:

* the SVG icon when uploading `res/img/svg/sharing-animated-dark-12.svg`. But maybe that's OK because it's fairly small.
* in the menu buttons, when the panel is dismissed
* the component showing up when doing drag and drop from a file
* The transition when reordering tracks
* The introduction on the search input
* Transitions in the active tab view, when opening tracks
* Possibly the transition when the "+" button appears when doing a selection
* The help about scrolling in Viewport

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-535)