Move AssetEntry implementation, too. #3000

Job	Run time
Documentation	11m 22s
Quick Checks	8s
ubuntu-22.04 / gcc / Debug	20m 16s
Linting	28m 12s
ubuntu-22.04 / gcc / RelWithDebInfo	28m 36s
windows-2022 / Debug	25m 5s
ubuntu-20.04 / clang / Debug	20m 10s
windows-2022 / RelWithDebInfo	29m 37s
ubuntu-20.04 / clang / RelWithDebInfo	25m 20s
macos-13 / clang / Debug	28m 10s
macos-13 / clang / RelWithDebInfo	14m 27s
	3h 51m 23s

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