[APM] Trace timeline: Multi-fold function doesn't update when all accordions are collapsed or expanded

[formgeist]

Summary

I noticed whenever you manually close the accordions the state of the multi-fold function at the top of the trace, doesn't update accordingly. Besides being a nice indicator for the function, the function is not working until you double click.

[elasticmachine]

Pinging @elastic/apm-ui (Team:apm)

[sorenlouv]

@cauemarcondes If you end up working on this I think it'll make sense to remove the local state from the waterfall items and instead have single state object on a higher level.

[formgeist]

Also new icons are incoming elastic/eui#3994