Use appendFrom in LazyValue.writeToParcel()

Due to lazy bundle, we can now have bundles touching the original parcel
(used to create the bundle in the first place) during serialization.
This can lead to races within the same bundle or across bundles when
the same is copied.

Both these cases happen in notification manager when it's about to post
notification for its listeners. In summary, it notifies all the
listeners in oneway calls and the listeners make a call back to
system_server to retrieve the notification. These calls back can race
and lead to the bug observed in http://b/198355758#comment12.

In order to avoid that we use appendFrom(mSource, mPosition) in
LazyValue.writeToParcel() since that method doesn't change or use the
cursor of mSource. We only ever write to mSource before creating all the
LazyValues, so there can't be any r/w races.

Test: 1. Attach debugger to system server and put log breakpoints in
         racy lines in Parcel$LazyValue.writeToParcel
      2. atest -d CtsHostsideNetworkTests:com.android.cts.net.HostsideRestrictBackgroundNetworkTests#testDozeModeMetered_enabledButWhitelistedOnNotificationAction
      3. Observe no crashes
Test: 1. Attach debugger as in previous "Test:" line
      2. Create a notification with a parcelable extra, post it
      3. Observe no crashes
Bug: 195622897
Bug: 198355758
Test: atest -d android.os.cts.ParcelTest android.os.cts.BundleTest android.os.BundleTest android.os.ParcelTest
Change-Id: I02f890d22910c69e29e791b55d3655962a6dddfd