Add `Mesh::merge` #36508

Job	Run time
build (windows-latest)	4m 10s
build (ubuntu-latest)	1m 55s
build (macos-latest)	5m 22s
ci	1m 41s
run-examples-on-windows-dx12	11m 41s
toml	9s
check-bevy-internal-imports	4s
check-doc	5m 30s
miri	6m 46s
check-missing-examples-in-docs	32s
check-missing-features-in-docs	27s
markdownlint	1m 9s
check-compiles	2m 15s
build-wasm	41s
msrv	45s
	43m 7s

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