Add WebView state restoration privacy feature (#1173)

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Please review the release process for BrowserServicesKit
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Task/Issue URL:
https://app.asana.com/0/1206226850447395/1209192796290067/f
iOS PR: duckduckgo/iOS#3838
macOS PR: duckduckgo/macos-browser#3752
What kind of version bump will this require?: Major

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**Description**:

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**Steps to test this PR**:
1. See steps for iOS: duckduckgo/iOS#3838

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**OS Testing**:

* [ ] iOS 14
* [ ] iOS 15
* [ ] iOS 16
* [ ] macOS 10.15
* [ ] macOS 11
* [ ] macOS 12

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Sources/BrowserServicesKit/PrivacyConfig/Features/PrivacyFeature.swift

@@ -67,6 +67,7 @@ public enum PrivacyFeature: String {
     case forceOldAppDelegate
     case htmlNewTabPage
     case tabManager
+    case webViewStateRestoration
 }
 
 /// An abstraction to be implemented by any "subfeature" of a given `PrivacyConfiguration` feature.