First draft of offchain phragmen weights (#6032)

* Fist draft of offchain weights

* Round of review feedback

* Update frame/staking/src/lib.rs

* Fix fuzzer

* Remove some redundant comment

* Weight refund for submit solution -- potentially revert.

* First version with custom trimming of the result.

* Update frame/staking/src/benchmarking.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* Update frame/staking/src/benchmarking.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* Apply suggestions from code review

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>
Co-authored-by: thiolliere <gui.thiolliere@gmail.com>

* Update frame/staking/src/benchmarking.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* Update frame/staking/src/benchmarking.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* Some improvements

* Benchmark submit solution without phragmen (PR for First draft of offchain phragmen weights) (#6073)

* implementation of new benchmark

* address comments

* replace test

* Update frame/staking/src/lib.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* update weight

* Fix refund

* Clean and rady for final bench

* Fix line-wdith

* Fix gitlab build

* Fix line-wdith

* Fix test macro

* Update frame/staking/src/lib.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* Update frame/staking/src/benchmarking.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* Better length check

* Update frame/staking/src/lib.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* Update final weight coefficients

* Update frame/staking/src/lib.rs

* Apply suggestions from code review

* Update frame/staking/src/testing_utils.rs

* Try and fix the line-width

* Revert "Try and fix the line-width"

This reverts commit b4e284727220085b9b3daf7682c4bbf29621da09.

* Try and fix the line-width the correct way

* Revert "Try and fix the line-width the correct way"

This reverts commit 04fce128e851c9584f9f0d708a5a73cae799d8c8.

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>
Co-authored-by: thiolliere <gui.thiolliere@gmail.com>
Co-authored-by: Gavin Wood <gavin@parity.io>

substrate/frame/support/src/lib.rs

@@ -218,6 +218,7 @@ macro_rules! assert_err_ignore_postinfo {
 	}
 }
 
+/// Assert an expression returns error with the given weight.
 #[macro_export]
 #[cfg(feature = "std")]
 macro_rules! assert_err_with_weight {