Ensure AIMapper and underlying IMPL outlive IMapperProvider

... as a

  static vendor::mapper::IMapperProvider<IMPL> provider;

may be destructed during a clean process exit (during __cxa_finalize())
but the underlying IMPL may still be in use on other threads.

Bug: b/304343434
Test: boot Cuttlefish
Change-Id: I80687494c61210d527908b5a67375950ca45c8ea