Fix incorrect publicHeaderPath in swift package (#1600)

Summary:
## Changes in this pull request

- The swift package works static type by default, so i removes static type in product library.
- If target's path is changed, it must manually specify the `publicHeaderPath`. I specifies the `publicHeaderPath` property.

### Checklist

- [x] All tests pass. Demo project builds and runs.
- [x] I added tests, an experiment, or detailed why my change isn't tested.
- [ ] I added an entry to the `CHANGELOG.md` for any breaking changes, enhancements, or bug fixes.
- [ ] I have reviewed the [contributing guide](https://github.com/Instagram/IGListKit/blob/main/.github/CONTRIBUTING.md)

Pull Request resolved: #1600

Test Plan:
Tested and confirmed this works with the iOS sample apps.

 {F1470046962}

Reviewed By: fabiomassimo

Differential Revision: D55006212

Pulled By: TimOliver

fbshipit-source-id: 2dae9e3bc68ad9a70fdb3f1892811d5725baf519

Package.swift

@@ -9,26 +9,25 @@ let package = Package(
     ],
     products: [
         .library(name: "IGListDiffKit",
-                 type: .static,
                  targets: ["IGListDiffKit"]),
         .library(name: "IGListKit",
-                 type: .static,
                  targets: ["IGListKit"]),
         .library(name: "IGListSwiftKit",
-                 type: .static,
                  targets: ["IGListSwiftKit"]),
     ],
     targets: [
         .target(
             name: "IGListDiffKit",
             path: "spm/Sources/IGListDiffKit",
-            resources: [.copy("PrivacyInfo.xcprivacy")]
+            resources: [.copy("PrivacyInfo.xcprivacy")],
+            publicHeadersPath: "include"
         ),
         .target(
             name: "IGListKit",
             dependencies: ["IGListDiffKit"],
             path: "spm/Sources/IGListKit",
-            resources: [.copy("PrivacyInfo.xcprivacy")]
+            resources: [.copy("PrivacyInfo.xcprivacy")],
+            publicHeadersPath: "include"
         ),
         .target(
             name: "IGListSwiftKit",