Documenting android/apex.go

Mostly documentation changes, but includes a few refactorings like
changing the variable names, reording functions, reordering statements
in logical order, etc.

Bug: 173472337
Test: m
Change-Id: I000c76e818722ed06bac03d9de87588b23552b08
diff --git a/apex/apex.go b/apex/apex.go
index ce323ca..dff0855 100644
--- a/apex/apex.go
+++ b/apex/apex.go
@@ -709,7 +709,7 @@
 		return true
 	})
 
-	apexContents := android.NewApexContents(mctx.ModuleName(), contents)
+	apexContents := android.NewApexContents(contents)
 	mctx.SetProvider(ApexBundleInfoProvider, ApexBundleInfo{
 		Contents: apexContents,
 	})