Make SharedAsset a base class, eliminate AssetContainer #2300

Job	Run time
Documentation	12m 3s
Quick Checks	12s
ubuntu-22.04 / gcc / Debug	6m 35s
ubuntu-22.04 / gcc / RelWithDebInfo	12m 8s
windows-2019 / Debug	7m 9s
ubuntu-20.04 / clang / Debug	6m 25s
ubuntu-20.04 / clang / RelWithDebInfo	10m 46s
windows-2019 / RelWithDebInfo	9m 55s
macos-12 / clang / Debug	8m 10s
windows-2022 / Debug	6m 53s
windows-2022 / RelWithDebInfo	9m 23s
macos-12 / clang / RelWithDebInfo	10m 21s
	1h 40m 0s

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