Contracts: Ensure latest migration match pallet_version (#14676)

* Add version check

* fix format

* simplify

* restructure imports

* add version check

* Fix benchmarking

* Rename migrations -> BenchMigrations

* doc

* add more docs

* fix format string

* Update frame/contracts/build.rs

* fix

* add cargo:rerun-if-changed

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Co-authored-by: parity-processbot <>