Test each benchmark case in own #[test] (#9860)

* Generate one #[test] fn per bench case.

* Update benchmark macro syntax in frame pallets.

* Explain new benchmark macro syntax in example pallet.

* support with and without a semicolon

* update pallets to use individual tests

* migrate staking too

* migrate more pallets

* fix up democracy and use individual tests

* Fix comment

* Put println message in panic

* Remove `another_set_dummy` from doc

`another_set_dummy` is not present in the benchmarking.rs (anymore).

* Update doc for benchmarks macro

* Update doc for impl_benchmark_test_suite macro

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>