ios: Add privacy manifest, copying deps' reasons for "required reason APIs"

[chrisbobbe]

Here's an attempt at #5847. It seems like we may have to manually aggregate our dependencies' reason codes and copy them into our own privacy manifest. See for example https://github.com/flutter/flutter/issues/145269#issuecomment-2070221423 :

We have observed a bug within App Store Connect that is mainly impacting SDKs distributed as static frameworks (which includes some Flutter plugins, or in the case of Flutter apps that do not use `use_frameworks!' almost all plugins) that declare required reasons in privacy manifests. Due to the bug, developers receive a warning from App Store Connect. We have raised this with Apple, who has acknowledged this issue and confirmed they are working on a fix. We will provide updates when available.

zulip-mobile's Podfile does not call use_frameworks!.

If we have to do this manual copying anyway, maybe it doesn't actually matter whether our dependencies come with the necessary privacy manifests? Maybe we can deal with #5847 with just this PR, then, and forget about the following PRs:

• 5856

• 5857

• 5858

Fixes: #5847

[chrisbobbe]

Cool, thanks for the review! Revision pushed. If the note in the commit message seems right, please go ahead and merge.

[gnprice]

Thanks! LGTM; merging.