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
diff --git a/android/packaging_test.go b/android/packaging_test.go
index 7269bfb..3d6fa43 100644
--- a/android/packaging_test.go
+++ b/android/packaging_test.go
@@ -73,7 +73,7 @@
 }
 
 func (m *packageTestModule) GenerateAndroidBuildActions(ctx ModuleContext) {
-	zipFile := PathForModuleOut(ctx, "myzip.zip").OutputPath
+	zipFile := PathForModuleOut(ctx, "myzip.zip")
 	m.entries = m.CopyDepsToZip(ctx, zipFile)
 }