Migrate `pallet-assets-freezer` to umbrella crate #9504

Job	Run time
preflight / preflight	45s
preflight / ci-versions	1m 2s
cargo-check-all-crate-macos	10m 45s
cargo-check-benches (master)	21m 6s
cargo-check-benches (current)	24m 44s
cargo-check-each-crate (1)	23m 40s
test-frame-ui	46m 43s
cargo-check-each-crate (2)	24m 26s
cargo-check-each-crate (3)	9m 47s
cargo-check-each-crate (4)	24m 2s
test-full-crypto-feature	2m 36s
test-node-metrics	11m 51s
cargo-check-each-crate (5)	34m 25s
cargo-check-each-crate (6)	15m 1s
cargo-check-each-crate (7)	34m 23s
test-frame-examples-compile-to-wasm	2m 59s
test-deterministic-wasm	7m 49s
check-tracing	2m 27s
check-metadata-hash	6m 54s
node-bench-regression-guard	17s
All test misc tests passed	1s
	5h 5m 43s

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