OGRWriter: Erase file prior to writing multiple layers to that same file

[Ylannl]

Sometimes we have the case where multiple OGRWriter write to various layers in the same file. There is an option to overwrite an entire layer (instead of appending to an existing layer). But this is slow, especially when it needs to happen for a huge number of files.

We need to implement a mechanism that deletes the entire file if it exists prior to writing the layers. This is already possible for the case with a single OGRWriter writing to on particular file. But there is a problem when multiple OGRWriters write to different layers in the same file, ie.it requires some coordination between multiple OGRWriter to ensure that the file is only deleted once and all the layers are present in the output file.