Use std::optional if available. #1996

Job	Run time
PSV.Linux.22.04.gcc11	8m 24s
PSV.Linux.Android.22.04	5m 22s
PSV.Linux.22.04.clang	8m 50s
PSV.iOS.MacOS13.Xcode15	14m 1s
PSV.MacOS13.Xcode15.x86_64	4m 33s
PSV.Linux.22.04.gcc9.Cpplint	8m 48s
PSV.Linux.latest.gcc14.OLP_SDK_ENABLE_DEFAULT_CACHE=OFF	3m 13s
PSV.Linux.22.04.gcc11.OLP_SDK_ENABLE_DEFAULT_CACHE=OFF	3m 4s
PSV.Linux.22.04.gcc13	12m 26s
PSV.MacOS14.Xcode15	2m 37s
PSV.Linux.22.04.gcc9.OLP_SDK_ENABLE_DEFAULT_CACHE=OFF	2m 35s
PSV.Linux.22.04.gcc9.Tests.CodeCov	10m 49s
PSV.iOS.MacOS13.Xcode14	12m 14s
PSV.MacOS15.Xcode16	8m 6s
PSV.iOS.MacOS15.Xcode16	5m 47s
PSV.Win.VC2022	11m 0s
PSV.iOS.MacOS14.Xcode15	5m 51s
PSV.Clang.Format.Checker	32s
PSV.Commit.Checker	5s
	2h 8m 17s

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