Restructure dispatch macro related exports (#1162)

* restructure dispatch macro related exports

* moved Dispatchable to lib.rs

* fix .gitignore final newline

* ".git/.scripts/commands/fmt/fmt.sh"

* fix rustdocs

* wip

---------

Co-authored-by: Liam Aharon <liam.aharon@hotmail.com>
Co-authored-by: command-bot <>
Co-authored-by: ordian <write@reusable.software>

substrate/frame/session/src/lib.rs

@@ -117,7 +117,7 @@ pub mod weights;
 
 use codec::{Decode, MaxEncodedLen};
 use frame_support::{
-	dispatch::{DispatchError, DispatchResult},
+	dispatch::DispatchResult,
 	ensure,
 	traits::{
 		EstimateNextNewSession, EstimateNextSessionRotation, FindAuthor, Get, OneSessionHandler,
@@ -129,7 +129,7 @@ use frame_support::{
 use frame_system::pallet_prelude::BlockNumberFor;
 use sp_runtime::{
 	traits::{AtLeast32BitUnsigned, Convert, Member, One, OpaqueKeys, Zero},
-	ConsensusEngineId, KeyTypeId, Permill, RuntimeAppPublic,
+	ConsensusEngineId, DispatchError, KeyTypeId, Permill, RuntimeAppPublic,
 };
 use sp_staking::SessionIndex;
 use sp_std::{