[ntuple] write streamer info of used types to ROOT file

[jblomer]

The file page sink, on commit, collects the streamer info records of custom classes. These records are passed together with the records from unsplit fields to the file writer, which will write them in the ROOT file streamer info record.

In the wake of this change, the minifile has been modified to let the ROOT streamers create the list of streamer info records. The hand-coded record for the RNTuple class was thus removed.

The change triggers / works around bug #15877

Fixes #14871

A separate PR to roottest should check the TFile::MakeProject() works as expected with RNTuple.