pallet-contracts: migrate to nested storage transaction mechanism (#6382)

* Add a simple direct storage access module

* WIP

* Completely migrate to the transactional system.

* Format

* Fix wasm compilation

* Get rid of account_db module

* Make deposit event eager

* Make restore_to eager

* It almost compiles.

* Make it compile.

* Make the tests compile

* Get rid of account_db

* Drop the result.

* Backport the book keeping.

* Fix all remaining tests.

* Make it compile for std

* Remove a stale TODO marker

* Remove another stale TODO

* Add proof for `terminate`

* Remove a stale comment.

* Make restoration diverging.

* Remove redudnant trait: `ComputeDispatchFee`

* Update frame/contracts/src/exec.rs

Co-authored-by: Alexander Theißen <alex.theissen@me.com>

* Introduce proper errors into the storage module.

* Adds comments for contract storage module.

* Inline `ExecutionContext::terminate`.

* Restore_to should not let sacrifice itself if the contract present on the stack.

* Inline `transfer` function

* Update doc - add "if succeeded"

* Adapt to TransactionOutcome changes

* Updates the docs for `ext_restore_to`

* Add a proper assert.

* Update frame/contracts/src/wasm/runtime.rs

Co-authored-by: Alexander Theißen <alex.theissen@me.com>

Co-authored-by: Alexander Theißen <alex.theissen@me.com>
Co-authored-by: Alexander Theißen <alexander.theissen@parity.io>