Allow "Anything" signal in inserter stack size

[ChickenBones]

Specifically, this would save combinators when sending a filter to an inserter with exactly one item. I can imagine there may be other places where being able to use Anything (or Everything and have it sum all signals) as inputs would make configuring things a bit easier.

This is similar to the suggestion for a setting to grab stack size exactly from the filter signal (posting.php?mode=reply&t=127037), which would be better for inserters specifically, but this doesn't require any UI changes.