This makes the collection logic of {Projection} nodes (i.e. value
projections for multi-value returning calls) more robust. The projection
nodes by now have a control input, which in turn can make them appear
more than once in the use list of a call. We should limit the use list
inspection to value edges only. This is in preparation of eliding any
redundant {IfSuccess} control node.

R=jarin@chromium.org

Change-Id: I9bb4cc0e2e877976be55a894af972aa83d07d7d7
Reviewed-on: https://chromium-review.googlesource.com/450244Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43608}