SI-8788 Add generic signature to Parcelable static field special case.

Android's AIDL generates Java code that assumes the presence of generic
annotations for Parcelable classes, which previously were not being
generated. This patch adds a generic signature to the generated CREATOR
field, resolving the issue.

Same as https://github.com/scala/scala/pull/3922 except into 2.11.x instead of 2.12.x.