Update API: initial support

Initial pieces of the Update API callback framework.

- move the status callback params to a new object, UpdateEngineStatus to
allow for the easier addition of new params in the future.
- switch the IUpdateEngineStatusCallback to provide a
ParcelableUpdateEngineStatus instead of a series of individual params
- move the various GetStatus() methods to use the UpdateEngineStatus
object instead of a series of params (which will need future expansion)
- Add current and new product/os versions to both the UpdateEngineStatus
and the ParcelableUpdateEngineStatus.

Bug: 64808702
Test: unit tests, and performing OTAs via a test app calling
  IUpdateEngine::AttemptUpdate() via UpdateManager::performUpdateNow()

Change-Id: I53f66f3511049f0809855814e1e758023cd8cc08
(cherry picked from commit 4f96ebf85022837603f2e10100a044d234b7d86f)
diff --git a/update_manager/fake_updater_provider.h b/update_manager/fake_updater_provider.h
index 44389f4..a7c15b5 100644
--- a/update_manager/fake_updater_provider.h
+++ b/update_manager/fake_updater_provider.h
@@ -53,7 +53,7 @@
     return &var_new_version_;
   }
 
-  FakeVariable<int64_t>* var_payload_size() override {
+  FakeVariable<uint64_t>* var_payload_size() override {
     return &var_payload_size_;
   }
 
@@ -100,7 +100,7 @@
     "stage", kVariableModePoll};
   FakeVariable<std::string> var_new_version_{  // NOLINT(whitespace/braces)
     "new_version", kVariableModePoll};
-  FakeVariable<int64_t> var_payload_size_{  // NOLINT(whitespace/braces)
+  FakeVariable<uint64_t> var_payload_size_{// NOLINT(whitespace/braces)
     "payload_size", kVariableModePoll};
   FakeVariable<std::string> var_curr_channel_{  // NOLINT(whitespace/braces)
     "curr_channel", kVariableModePoll};