LineSegmentIndex: Avoid creating std::vector on heap #2935

Job	Run time
Windows (mingw-w64, Debug, 11, x86_64, windows-2019)	12m 7s
Windows (mingw-w64, Release, 11, x86_64, windows-2019)	8m 36s
Linux (g++, Coverage, 11, 64, g++, 3.15.*, -DBUILD_BENCHMARKS=ON, ubuntu-20.04)	6m 40s
Linux (clang++, Release, 11, 64, clang, 3.13.*, ubuntu-20.04)	5m 33s
CMake Subproject	2m 25s
Windows (Visual Studio 2019, Release, windows-2019)	9m 7s
Windows (Visual Studio 2022, Debug, windows-2022)	10m 10s
Linux (clang++, Debug, 11, 64, clang, 3.17.*, ubuntu-20.04)	6m 6s
Linux (clang++, Release, 14, 64, clang, 3.17.*, ubuntu-20.04)	5m 46s
Linux (g++, Release, 11, 64, g++, 3.22.*, ubuntu-22.04)	5m 18s
	1h 11m 48s

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