remove use of mach_absolute_time (#15554)

`mach_absolute_time` is one of Apple's required reason APIs (https://developer.apple.com/documentation/kernel/1462446-mach_absolute_time?language=objc). Replace it with the suggested `clock_gettime_nsec_np(CLOCK_UPTIME_RAW)` so that we don't need a RRA entry in a privacy manifest.

issue #15029

Closes #15554

COPYBARA_INTEGRATE_REVIEW=https://github.com/protocolbuffers/protobuf/pull/15554 from protocolbuffers:dmaclach-mach_absolute_time 295d83178d
PiperOrigin-RevId: 601370915

src/google/protobuf/map.h

@@ -25,7 +25,7 @@
 #include <utility>
 
 #if !defined(GOOGLE_PROTOBUF_NO_RDTSC) && defined(__APPLE__)
-#include <mach/mach_time.h>
+#include <time.h>
 #endif
 
 #include "google/protobuf/stubs/common.h"
@@ -691,7 +691,7 @@ class PROTOBUF_EXPORT UntypedMapBase {
 #if defined(__APPLE__)
     // Use a commpage-based fast time function on Apple environments (MacOS,
     // iOS, tvOS, watchOS, etc).
-    s += mach_absolute_time();
+    s = clock_gettime_nsec_np(CLOCK_UPTIME_RAW);
 #elif defined(__x86_64__) && defined(__GNUC__)
     uint32_t hi, lo;
     asm volatile("rdtsc" : "=a"(lo), "=d"(hi));