Allow CopyDepsToZip() to work on WritablePath

Makes the method more generally usable as it can work with any
WritablePath not just OutputPath. Also, makes it independent of whether
PathForModuleOut() returns ModuleOutPath or OutputPath.

Bug: 179124768
Test: m nothing
Change-Id: I08e61a24722198aa92fa2f8a2d096b1a8bf9c5c2