Use git log name-status in get last commit (#16059)

* Improve get last commit using git log --name-status

git log --name-status -c provides information about the diff between a
commit and its parents. Using this and adjusting the algorithm to use
the first change to a path allows for a much faster generation of commit
info.

There is a subtle change in the results generated but this will cause
the results to more closely match those from elsewhere.

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: Lauris BH <lauris@nix.lv>

modules/indexer/code/bleve.go

@@ -216,6 +216,9 @@ func (b *BleveIndexer) addUpdate(batchWriter git.WriteCloserError, batchReader *
 		return nil
 	}
 
+	if _, err = batchReader.Discard(1); err != nil {
+		return err
+	}
 	id := filenameIndexerID(repo.ID, update.Filename)
 	return batch.Index(id, &RepoIndexerData{
 		RepoID:    repo.ID,