Add Swift Package Manager support (Fixes #7047)

[UInt2048]

Creates Package.swift to fix #7047

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[thomasvl]

How does path, exclude, and sources all work together? There are sources needed that don't live under that sources reference. I don't suppose there's any way to use globs to help cut down on what has to be explicitly listed?

[ydnar]

@thomasvl unfortunately, no globbing. You can use more explicit sources, or explicit exclude. For example: https://github.com/getsentry/sentry-cocoa/pull/352/files

[thomasvl]

Also, how do we test things to be sure things are working? We're also seeing some issue with CocoaPods around case sensitive/case insensitive file systems (#6803) and how it handles the path names. So if we are looking to add SwiftPM support, it would be nice to sure things are working for all setups.

[UInt2048]

One way you can test is by adding it as a package in a dependent Xcode project. I don’t know what globs are, and there are a lot of files in this repository, but I just wanted to get something started if I could.

[thomasvl]

One way you can test is by adding it as a package in a dependent Xcode project within Xcode. I don’t know what globs is, and there are a lot of files in this repository, but I just wanted to get something started if I could.

globs are patterns like *.m and some systems allow them to be recursive so you don't have to list paths. They are used in the podspec to make it easier to list what is needed without having to have something like the excludes.

As far as getting something started, once it lands, it has to be supported. So we need to be sure it is going to work correctly for all cases, hence seeing what can be done to test it, etc. Otherwise, it might work for some folks but not others, and in some ways that ends up being worse than not having support.

[UInt2048]

OK, I would love to see support, but I understand the need to make it work for all test cases. Happy New Year!

Maintainers, please add release notes: no label

[UInt2048]

Closing because:

1. It doesn't seem to be gaining acceptance
2. https://github.com/apple/swift-protobuf has had SwiftPM support since the beginning

If anyone believes it should be reopened, it's always a possibility!