Add a longpress timeout config for screenshot chord

The global actions longpress timeout is currently used for the
screenshot chord. This means that increasing the globalactions
longpress timeout would also increase the time for triggering
a screenshot.

This adds a configuration item specifically for the screenshot
chord.

Bug: 119989329
Test: manual - increase the globalactions timeout and check that
               the screenshot chord is not affected.
Change-Id: I6bd8416f7546aa1d2da43f37f3e76edac3ed543b