Support an action table that shows longest running actions

If SOONG_UI_TABLE_HEIGHT is set, enable a new smart terminal display
that prints the normal scrolling build history in the top region of
the screen and an action table of the longest currently running
actions in the bottom region of the screen.  This provides better
visibility into which are the longest running actions and when the
build parallelism is very low.

Test: manual
Change-Id: I677d7b6b008699febd259110d7f9e0f98d80c535