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/sideload_main.cc b/sideload_main.cc
index 574d062..52f045e 100644
--- a/sideload_main.cc
+++ b/sideload_main.cc
@@ -42,6 +42,7 @@
 using std::string;
 using std::vector;
 using update_engine::UpdateStatus;
+using update_engine::UpdateEngineStatus;
 
 namespace {
 // The root directory used for temporary files in update_engine_sideload.
@@ -81,11 +82,10 @@
   }
 
   // ServiceObserverInterface overrides.
-  void SendStatusUpdate(int64_t last_checked_time,
-                        double progress,
-                        UpdateStatus status,
-                        const string& new_version,
-                        int64_t new_size) override {
+  void SendStatusUpdate(
+      const UpdateEngineStatus& update_engine_status) override {
+    UpdateStatus status = update_engine_status.status;
+    double progress = update_engine_status.progress;
     if (status_ != status && (status == UpdateStatus::DOWNLOADING ||
                               status == UpdateStatus::FINALIZING)) {
       // Split the progress bar in two parts for the two stages DOWNLOADING and