Intersection of PdfReader and PdfWriter

[j-t-1]

It may be good to decrease the symmetric difference of PdfReader and PdfWriter functionality.

Two examples:

1. PdfWriter has generate_file_identifiers, but PdfReader does not have file_identifiers?
2. PdfWriter has open_destination, but PdfReader does not?

For 1. what is the current way of reading the file identifiers?
For 2. is there a reason for this?

[stefan6419846]

In #2497, we started working on unifying the code between both classes, thus some oddities might be resolved in the future.

There probably is not much to tell about the reasoning for why one class does it like this and the other class another way. Primarily write-specific functionality might be available inside the writer only, which makes sense.

With #2495, the reader got the _ID property you were asking for - although this might break without warning due to not being part of the public API.

[j-t-1]

Kudos for already having done most of this. If there is a list of potential things still to unify these two could be appended.