QQmlJS::Dom::OwningItem should use UTC date stamps

$ ./qtbase/tests/benchmarks/corelib/time/qdatetime/tst_bench_qdatetime currentDateTime{,Utc}
********* Start testing of tst_QDateTime *********
Config: Using QtTest library 6.4.0, Qt 6.4.0 (x86_64-little_endian-lp64 shared (dynamic) release build; by Clang 10.0.0 ), ubuntu 20.04
PASS   : tst_QDateTime::initTestCase()
PASS   : tst_QDateTime::currentDateTime()
RESULT : tst_QDateTime::currentDateTime():
     1.1 msecs per iteration (total: 75, iterations: 64)
PASS   : tst_QDateTime::currentDateTimeUtc()
RESULT : tst_QDateTime::currentDateTimeUtc():
     0.033 msecs per iteration (total: 69, iterations: 2048)
PASS   : tst_QDateTime::cleanupTestCase()
Totals: 4 passed, 0 failed, 0 skipped, 0 blacklisted, 613ms
********* Finished testing of tst_QDateTime *********