java.Module is using "Custom" function to write Android.mk.
And if "hostdex" is set to "true", it writes "hostdex" module definition
as well as original module.
As of now, Required/Host_required/Target_required props are filled in
the AndroidMkEntries structure(aosp/939505). But these are not
passed to old AndroidMkData.Custom function.
So, if a java_library declares "hostdex:true" and "required:[...]"
together, "required" is not applied to the "hostdex" variant.
This change copies *Required props from AndroidMkEntries to
AndroidMkData before calling its Custom callback.
Test: m (runs soong unit tests)
Change-Id: I5f85714f721a2a0917ab18072dbea52294c770e7
