Use std::optional if available. #1997

Job	Run time
PSV.Linux.22.04.gcc9.Tests.CodeCov	10m 37s
PSV.Linux.22.04.gcc9.Cpplint	9m 24s
PSV.Linux.Android.22.04	5m 59s
PSV.Linux.22.04.clang	8m 45s
PSV.Linux.latest.gcc14.OLP_SDK_ENABLE_DEFAULT_CACHE=OFF	3m 3s
PSV.Linux.22.04.gcc11.OLP_SDK_ENABLE_DEFAULT_CACHE=OFF	2m 38s
PSV.Linux.22.04.gcc13	16m 24s
PSV.MacOS14.Xcode15	5m 32s
PSV.MacOS13.Xcode15.x86_64	3m 10s
PSV.MacOS15.Xcode16	7m 19s
PSV.Linux.22.04.gcc9.OLP_SDK_ENABLE_DEFAULT_CACHE=OFF	2m 39s
PSV.Linux.22.04.gcc11	8m 10s
PSV.Win.VC2022	9m 39s
PSV.iOS.MacOS14.Xcode15	7m 6s
PSV.iOS.MacOS13.Xcode15	10m 54s
PSV.iOS.MacOS15.Xcode16	9m 2s
PSV.Commit.Checker	7s
PSV.iOS.MacOS13.Xcode14	12m 44s
PSV.Clang.Format.Checker	33s
	2h 13m 45s

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