Export PrivacyInfo.xcprivacy (#17054)

Export `PrivacyInfo.xcprivacy` file to allow users of protobuf to access the file from Bazel, e.g. to bundle it with an iOS application.

Closes #17054

COPYBARA_INTEGRATE_REVIEW=https://github.com/protocolbuffers/protobuf/pull/17054 from mjburghard:export-privacy-manifest 4869cabc3d
PiperOrigin-RevId: 647791805

BUILD.bazel

@@ -12,7 +12,10 @@ load(":protobuf.bzl", "internal_objc_proto_library", "internal_php_proto_library
 
 licenses(["notice"])
 
-exports_files(["LICENSE"])
+exports_files([
+    "LICENSE",
+    "PrivacyInfo.xcprivacy",
+])
 
 ################################################################################
 # Well Known Types Proto Library Rules