Apply `WeightToFeePolynomial`s to `pallet_transaction_payment`'s length fee (#10785)

* Apply WeightToFeePolynomials to length fee

* Remove TransactionByteFee

* Add test cases for ConstantModifierFee

* Restore import

* Use pallet::constant_name

* Remove irrelevant TODO comment

* Update frame/support/src/weights.rs

* Update frame/transaction-payment/src/lib.rs

* Update frame/transaction-payment/src/lib.rs

* Update frame/transaction-payment/src/lib.rs

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* s/ConstantModifierFee/ConstantMultiplier/

* Impl LengthToFee for test configs

* fmt

* Remove unused import

* Impl WeightToFeePolynomial for byte fee in ExtBuilder

* Remove unused import

* fix doc

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>
Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>