clean up exported source format (#28129)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28129
The previous PR in the stack removed the need to order classes/functions
or have correct import statements. This resolved circular depedency issues
that can arise when class constructors like ModuleList put new instances
of themselves in a common namespace.
This PR changes our export format to no longer produce this information.
By doing so we can make the logic signficantly simpler, since we just
keep track of an individual PythonPrint object per file.
Notes:
* PythonPrint was changed to manage its own stream/list of ranges. It
was doing this anyway internally, this just makes the API more clear.
* Since we are changing the serialization format, I also removed op_version_set.
It is now replaced with the VERSION number that written in the zip archive.
This further simplifies the code emission process.
* A test of op_version_set was removed since there is no longer any behavior
to test.
Test Plan: Imported from OSS
Differential Revision: D17961610
Pulled By: zdevito
fbshipit-source-id: ada362c4ca34d05393a1a7e799c94785ab9d9825
