Allow duplicate types from preprocessed

When compiling for SDK stub sources, we need to load documents which are
also a part of preprocessed framework.aidl, which results in inevitable
type duplication.

We allow duplicate types only if one of them is from preprocessed
document.

Bug: 192211616
Test: aidl_unittests
Change-Id: I21fc66d7305df824d2cc84308b84b9c9e9213d13
8 files changed