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/tests/test_debug.rs

@@ -18,10 +18,10 @@
 use super::*;
 use crate::{
 	debug::{CallInterceptor, CallSpan, ExecResult, ExportedFunction, Tracing},
+	primitives::ExecReturnValue,
 	AccountIdOf,
 };
 use frame_support::traits::Currency;
-use pallet_contracts_primitives::ExecReturnValue;
 use pretty_assertions::assert_eq;
 use std::cell::RefCell;