`srml_support` storage reorganize (#3344)

* impl

* file split

* old comment

* better error message

* WIP

* basti test works

* comment

* remove old files

* impl swap for storage map

* fix

* fix and comment

* code refactor

* code refactor

* code format

* code refactor

* fix

* fix

* fix

* document generators

* license

* doc

* doc

* fmt

Co-Authored-By: Bastian Köcher <[email protected]>

* some comment addressed

* storage_items small refactor

* fix storage_items

* more precise returned type

* fix

* code fmt suggestion

Co-Authored-By: Bastian Köcher <[email protected]>

* remove box allocation

* bump version

* rename function as behavior has changed

* fix doc