Actual SI-6555 fix, Scaladoc filter works WITH keyboard shortcuts too

Commit daefab18b8b0c170c372991022357413ec69b2af attempted to fix a bug
related to Scaladoc filtering, meanwhile breaking Scaladoc keyboard
shortcuts.

Before commit daefab18b8b0c170c372991022357413ec69b2af, Scaladoc's
filter wouldn't consider the last character of a search term entered
into the (left) Scaladoc filter pane, but toggling with the `tab` key
between filter panes did work.

After daefab18b8b0c170c372991022357413ec69b2af, Scaladoc's left pane
filter correctly searches for the full search term, but pressing the
`tab` key causes the "focus" of the input bar to be stuck on the
filter panel in the right Scaladoc filter pane, rendering it useless.

End result: annoying Scaladoc interface bug present in 2.10.1, but
which wasn't present in 2.10.0.

This pull request fixes this, enabling both behaviors. The `tab` key
toggle needed to be triggered on a `keydown` event (currently it's
not), while everything else is fine to be triggered on a `keyup`
event. This pull request enables the correct behavior by binding both
a `keydown` and a `keyup` event rather than lumping everything all
together in a `keyup` event (as was the case before).
Merge pull request #2515 from heathermiller/issue/6555

Actual SI-6555 fix, Scaladoc filter works now WITH keyboard shortcuts too