GPUUploadManagerImpl: seal free pages to prevent stale-thread (ABA) w… #4244

Job	Run time
Linux -> Pre-checks	17s
Linux -> Clang-x64, Release	12m 59s
Linux -> Clang-NO_GLSLANG-x64, Debug	8m 10s
Linux -> Clang-NO_GLSLANG-NO_HLSL-x64, Release	5m 30s
Linux -> GCC-x64, Release	10m 48s
Linux -> Clang-x64, Debug	13m 15s
Linux -> GCC-x64, Debug	11m 53s
	1h 2m 52s

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