Bazel: add codeql specific packaging library

[redsun82]

This encapsulate arch specific logic, local installation and separation of zip files into generic and arch-specific parts as required by the internal build. The logic behind separating generic and arch-specific files lies in using {CODEQL_PLATFORM} in the prefix, which then gets expanded to the appropriate value.

Moreover, this PR the ability to import .zip files into the pack in a highly optimized way:

• when installing the pack, ripunzip will be used to unzip the zip file contents to the destination prefix
• when creating a zip file of the pack, a special purpose zipmerge (ported from the internal repository) merges the imported zips into the output, without decompressing.

These changes are applied to swift as an example.

[criemen]

Thanks! some initial comments, a lot of them around missing documentation. I'll take a second look at the rule implementation once the documentation is there, so I have a better idea how things are supposed to hang together.

[criemen]

One more round of review comments, thanks a lot for all the code comments, they've been really useful in following along.

[criemen]

Is there a need to expose this separately from zips?
Couldn't we just merge the zip files in zips? I don't see the benefit of a base argument, but happy to be convinced.

[redsun82]

ah, after trying it again I remembered why I had done this. The distinction whether to select a zip or not depends on its prefix containing {CODEQL_PLATFORM}. The base zip would be added with an empty "" prefix, which would disqualify it from the arch zipmerge. So the base_zip is always included, while zips are included conditionally.

[criemen]

Ah, then a comment to that effect would be great, to explain that design choice to future us.

[criemen]

Thanks a lot, I think we're nearly there ❤️

[criemen]

Can we pull out this logic into a variable in codeql_pack, and remove the same/similar filename scheme from _zipmerge? That'd make zipmerge a little bit more generic, too.

[redsun82]

such an innocent looking comment 😝

I've ended up extracting the whole filtering + plat expansion logic to separate rules with a specific provider. This effectively seems like being on the good path to generalize _zipmerge now.