Add PrivacyInfo.xcprivacy to plugin template

[stuartmorgan]

Adds an empty privacy manifest, and commented out code to include it in the build, to the plugin template. This will make it much easier to explain how to add a privacy manifest in plugin docs, since instead of explaining the format of the file from scratch and providing example code to inculde it, we can just instruct people to add entries to an exisitng file and then uncomment a line or two. This will also make it much easier to figure out from the template output itself how to add support for people who don't find the documentation.

Part of #131940

Fixes #140013

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• I followed the breaking change policy and added Data Driven Fixes where supported.
• All existing and new tests are passing.

[stuartmorgan]

This is gross, but because the parameters are order-specific and trailing commas aren't allowed, I couldn't see any other option.

I tried using excludes so this wouldn't be conditional at all, but that caused build failures for some reason (maybe due to everything being excluded?)

[vashworth]

Could put the comment inside and just comment out the .process("Resources"), line.

            dependencies: [], 
            resources: [
                        // If your plugin requires a privacy manifest, for example if it uses any required
                        // reason APIs, update the PrivacyInfo.xcprivacy file to describe your plugin's privacy
                        // impact, and then uncomment these lines. For more information, see
                        // https://developer.apple.com/documentation/bundleresources/privacy_manifest_files
                        //     .process("Resources"),
            ]

[vashworth]

Also, the Resources folder is also where images and other resource files go, the comment kind of seems like it's only used for privacy manifests.

Maybe change to something like
"If your plugin uses resource files or requires a privacy manifest, uncomment the line below. If your plugin does not require a privacy manifest, delete the PrivacyInfo.xcprivacy file provided in the Resources directory. If your plugin does requires a privacy manifest, for example if it uses any required reason APIs, update the PrivacyInfo.xcprivacy file to describe your plugin's privacy impact. For more information, see https://developer.apple.com/documentation/bundleresources/privacy_manifest_files"

Idk, that's kind of long, though. We could also put the privacy manifest in a different spot so it's independent of other Resources

[jmagman]

So hopefully it's a niche situation they would have anything else in resources. I don't have a preference.

[stuartmorgan]

Could put the comment inside and just comment out the .process("Resources"), line.

I thought I had tried that and gotten the same error as when I did exclude, but I must be misremembering since it works for me now.

Also, the Resources folder is also where images and other resource files go, the comment kind of seems like it's only used for privacy manifests.

Yes, I'd thought about that too, but when I had tried to make the comment cover everything it seemed like kind of a mess.

We could also put the privacy manifest in a different spot so it's independent of other Resources

Ooh, I like that. I hadn't considered that option; I'll set it up that way (and re-test to be sure it's working).

Do we want to keep the empty Resources folder at that point? I would be tempted to just put a comment saying other files or directories could be added if they happened to need other resources, since I don't think it's common.

[stuartmorgan]

Updated to unconditionally have resources:, and moved the privacy manifest to a stand-alone file that is added to resources by a single commented-out line.

I also removed Resources and just put a comment since:

• I think having other resources will be rare,
• there's now an example right there someone can refer to if they need to see how it works, and
• it completely avoids the whole .gitkeep issue with pub.

[vashworth]

fyi @jmagman

[jmagman]

LGTM whenever @vashworth is happy. Thanks for doing this!
(linked this PR to close #140013)

[jmagman]

So hopefully it's a niche situation they would have anything else in resources. I don't have a preference.

[stuartmorgan]

You may want to adjust your migration instruction comment to match this structure, just for consistency.

[vashworth]

LGTM