Move IndentingPrintWriter to android.util

The old implementation remains in its place for now.

IndentingPrintWriter is still hidden - it will be made public
separately.

Test: atest FrameworksUtilTests:android.util.IndentingPrintWriterTest
Bug: 142281756

Change-Id: Idd2bfa027733ef384b5a676866a89fb3c35b06cb