Add PrivacyInfo.xcprivacy (protocolbuffers#15557)

issue#protocolbuffers#15029

As required by https://developer.apple.com/support/third-party-SDK-requirements/

Protos does not collect data.

Required reason APIs searched for using:
```
grep -ER 'NSFileCreationDate|NSFileModificationDate|fileModificationDate|NSURLContentModificationDateKey|NSURLCreationDateKey|getattrlist\(|getattrlistbulk\(|fgetattrlist\(|stat\(|fstat\(|fstatat\(|lstat\(|getattrlistat\(|systemUptime\(|mach_absolute_time\(|NSURLVolumeAvailableCapacityKey|NSURLVolumeAvailableCapacityForImportantUsageKey|NSURLVolumeAvailableCapacityForOpportunisticUsageKey|NSURLVolumeTotalCapacityKey|NSFileSystemFreeSize|NSFileSystemSize|statfs\(|statvfs\(|fstatfs\(|fstatvfs\(|getattrlist\(|fgetattrlist\(|getattrlistat\(|activeInputModes|NSUserDefaults' .
```

```
./third_party/utf8_range/utf8_to_utf16/main.c:    if (fstat(fd, &stat) == -1) {
./third_party/utf8_range/main.c:    if (fstat(fd, &stat) == -1) {
./src/google/protobuf/map.h:    s = mach_absolute_time();
./src/google/protobuf/io/io_win32.cc:int stat(const char* path, struct _stat* buffer) {
./src/google/protobuf/io/io_win32.cc:  return ::_wstat(wpath.c_str(), buffer);
./src/google/protobuf/io/io_win32.cc:  return ::_stat(path, buffer);
./src/google/protobuf/io/io_win32.h:PROTOBUF_EXPORT int stat(const char* path, struct _stat* buffer);
./src/google/protobuf/testing/file.cc:  if (lstat(name.c_str(), &stats) != 0) return;
./src/google/protobuf/compiler/importer.cc:    ret = stat(std::string(filename).c_str(), &sb);
```

`./third_party/utf8_range/...` - tool for utf that is not in user binaries
`./src/google/protobuf/map.h` - resolved with pull#15554
`./src/google/protobuf/io/io_win32.cc` - windows code
`./src/google/protobuf/testing/file.cc` - testing code not in user binaries
`./src/google/protobuf/compiler/importer.cc` - compiler code not in user binaries

So no required reason APIs.

Apple has not yet communicated how this is to be put into podspecs so saving for future commit.

Closes protocolbuffers#15557

COPYBARA_INTEGRATE_REVIEW=protocolbuffers#15557 from dmaclach:privacy 4c4e570
PiperOrigin-RevId: 601362376

PrivacyInfo.xcprivacy

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>NSPrivacyTracking</key>
+	<false/>
+	<key>NSPrivacyTrackingDomains</key>
+	<array/>
+	<key>NSPrivacyCollectedDataTypes</key>
+	<array/>
+	<key>NSPrivacyAccessedAPITypes</key>
+	<array/>
+</dict>
+</plist>