Support IsDeltaPayload per <package>.

Mixed full and delta payloads are now supported for multi-payload.

Bug: 36252799
Test: update_engine_unittests
Change-Id: Ic519f8399579c714a65ba9f9f948a389fcc249ed
(cherry picked from commit 4928112f8635f7a5b583171640aee2bda690ba34)
diff --git a/payload_consumer/download_action_unittest.cc b/payload_consumer/download_action_unittest.cc
index 9d85550..7d3ac6c 100644
--- a/payload_consumer/download_action_unittest.cc
+++ b/payload_consumer/download_action_unittest.cc
@@ -141,8 +141,8 @@
 
   uint64_t size = data.size() - 1;
   InstallPlan install_plan;
-  install_plan.payload_type = InstallPayloadType::kDelta;
-  install_plan.payloads.push_back({.size = size});
+  install_plan.payloads.push_back(
+      {.size = size, .type = InstallPayloadType::kDelta});
   // We pull off the first byte from data and seek past it.
   EXPECT_TRUE(HashCalculator::RawHashOfBytes(
       &data[1], data.size() - 1, &install_plan.payloads[0].hash));