Implement object checkout in PrepareCheckout #4489

Job	Run time
installation (win-msvc)	6m 25s
pure-rust-build	2m 4s
installation (win-gnu)	6m 50s
installation (win32-msvc)	6m 22s
test	22m 28s
installation (win32-gnu)	5m 53s
test-32bit (armv7-linux-androideabi)	1m 8s
test-fast (windows-latest)	14m 28s
cargo-deny (advisories)	28s
check-packetline (ubuntu-latest)	5s
test-fast (macos-latest)	2m 18s
cargo-deny (bans licenses sources)	30s
test-fast (ubuntu-latest)	3m 18s
lint	3m 57s
WebAssembly (wasm32-unknown-unknown)	52s
WebAssembly (wasm32-wasi)	37s
	1h 17m 43s

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