Add 'garbage collection' hold when receive late element

[damccorm]

We currently add a 'garbage collection' hold in WatermarkHold (invoked via ReduceFnRunner) if the closing behavior is FIRE_ALWAYS. This means an element which has come in too late for a data holds and an end-of-window hold may end up setting no hold at all. As a result, the eventual pane containing that element may end up dropped as being too late.

Imported from Jira BEAM-311. Original Jira may contain additional context.
Reported by: mshields822.