Contracts: use compiled rust tests (#2347)

see #2189

This PR does the following:
- Bring the user api functions into a new pallet-contracts-uapi (They
are currently defined in ink!
[here])(https://github.com/paritytech/ink/blob/master/crates/env/src/engine/on_chain/ext.rs)
- Add older api versions and unstable to the user api trait.
- Remove pallet-contracts-primitives and bring the types it defined in
uapi / pallet-contracts
- Add the infrastructure to build fixtures from Rust files and test it
works by replacing `dummy.wat` and `call.wat`
- Move all the doc from wasm/runtime.rs to pallet-contracts-uapi.

This will be done in a follow up:
- convert the rest of the test from .wat to rust
- bring risc-v uapi up to date with wasm
- finalize the uapi host fns, making sure everything is codegen from the
source host fns in pallet-contracts

---------

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

substrate/frame/contracts/mock-network/src/tests.rs

@@ -29,9 +29,8 @@ use frame_support::{
 	traits::{fungibles::Mutate, Currency},
 };
 use pallet_balances::{BalanceLock, Reasons};
-use pallet_contracts::{CollectEvents, DebugInfo, Determinism};
+use pallet_contracts::{Code, CollectEvents, DebugInfo, Determinism};
 use pallet_contracts_fixtures::compile_module;
-use pallet_contracts_primitives::Code;
 use xcm::{v3::prelude::*, VersionedMultiLocation, VersionedXcm};
 use xcm_simulator::TestExt;