Implemented the RoundUint64ToFloat64 TurboFan operator for x64 and arm64.

test/cctest/compiler/test-run-machops.cc

Index: test/cctest/compiler/test-run-machops.cc
diff --git a/test/cctest/compiler/test-run-machops.cc b/test/cctest/compiler/test-run-machops.cc
index 038fe241ebaf839ee49ef2a3e3a3ccc99f2e7986..b975b85330af2ed78773a7a30df140ef81de7eb0 100644
--- a/test/cctest/compiler/test-run-machops.cc
+++ b/test/cctest/compiler/test-run-machops.cc
@@ -5381,6 +5381,13 @@ TEST(RunRoundInt64ToFloat64) {
 }
 
 
+TEST(RunRoundUint64ToFloat64) {
+  BufferedRawMachineAssemblerTester<double> m(kMachUint64);
+  m.Return(m.RoundUint64ToFloat64(m.Parameter(0)));
+  FOR_UINT64_INPUTS(i) { CHECK_EQ(static_cast<double>(*i), m.Call(*i)); }
+}
+
+
 #endif