3988 [in_app_purchase] Fix Restore previous purchases link (cla: yes, waiting for tree to go green, p: in_app_purchase)

4005 Standardize XCTest locations and harnesses (cla: yes, p: webview_flutter, p: camera, p: google_sign_in, p: image_picker, p: in_app_purchase, p: local_auth, platform-ios)

4008 [in_app_purchase] Explanation for casting details to implementations (cla: yes, waiting for tree to go green, p: in_app_purchase)

4020 [in_app_purchase] Added userIds to google play purchase (cla: yes, waiting for tree to go green, p: in_app_purchase, platform-android)