Pack multiple meshes into vertex and index buffers. #44811

Job	Run time
build (windows-latest)	1m 10s
build (ubuntu-latest)	1m 25s
check-bevy-internal-imports	4s
build (macos-latest)	1m 8s
check-cfg	1m 9s
check-doc	9m 45s
check-missing-examples-in-docs	28s
ci	1m 52s
miri	6m 46s
run-examples-macos-metal	4m 37s
toml	1m 54s
typos	9s
check-missing-features-in-docs	31s
markdownlint	1m 12s
msrv	0s
build-wasm	0s
build-wasm-atomics	0s
check-compiles	0s
	32m 10s

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