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/src/benchmarking/mod.rs

@@ -33,7 +33,6 @@ use crate::{
 	migration::{
 		codegen::LATEST_MIGRATION_VERSION, v09, v10, v11, v12, v13, v14, v15, MigrationStep,
 	},
-	wasm::CallFlags,
 	Pallet as Contracts, *,
 };
 use codec::{Encode, MaxEncodedLen};
@@ -46,6 +45,7 @@ use frame_support::{
 };
 use frame_system::RawOrigin;
 use pallet_balances;
+use pallet_contracts_uapi::CallFlags;
 use sp_runtime::traits::{Bounded, Hash};
 use sp_std::prelude::*;
 use wasm_instrument::parity_wasm::elements::{BlockType, Instruction, ValueType};