fix: Break up big files in `types` directory

[m-strzelczyk]

Fixes #1252

Dividing the classes for each proto into 3 separate files:

• %proto/requests.py.j2
• %proto/responses.py.j2
• %proto/init.py.j2

The division is pretty simple. All "...Request" classes go to requests.py file, all "...Response" classes go to responses.py and everything else goes to other.py. This way, the content should be spread across multiple files and will move us away from the 2.5Mb PyCharm limit.

For comparison, in current version of python-compute, which I suspect might be the biggest GAPIC API library, the types/compute.py file is 2.8Mb big. After the change, we have:

• %proto/requests.py - 1.5Mb
• %proto/responses.py - 15Kb
• %proto/init.py - 1.4Mb

This change gives us 1Mb distance from the 2.5Mb limit and should last relatively long.

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Fixes #1252 🦕

[m-strzelczyk]

I tested this by replacing google/cloud/compute/types directory in my local python-compute installation by the types directory generated with this change. It worked fine.

[vchudnov-g]

Thanks for doing this, @m-strzelczyk ! I have one overall question: what was your rationale for choosing to do a separation based on requests/responses/other as opposed to a separation based on proto service name? Naively, it seems to me the latter keeps related things closer together and is (arguably) more robust if "other" becomes really big itself, or if there is a change to naming conventions.

[m-strzelczyk]

@vchudnov-g I agree that it would be nice to sort the types the same way we sort services, however I found it too complicated for me. The types all come from a single file from the googleapis/googleapis repository (in case of Compute that would be file google/cloud/compute/v1/compute.proto). In this file, there's no division, it's just one big bag of types that are used by GCE API. That's why I decided on this arbitrary division into Requests, Responses and others. This division logic is simple and can be easily changed if we decide that it's not working.