seal: Fix and improve error reporting (#6773)

* seal: Rework ext_transfer, ext_instantiate, ext_call error handling

* Deny calling plain accounts (must use transfer now)
* Return proper module error rather than ad-hoc strings
* Return the correct error codes from call,instantiate (documentation was wrong)
* Make ext_transfer fallible again to make it consistent with ext_call

* seal: Improve error messages on memory access failures

* seal: Convert contract trapped to module error

* seal: Add additional tests for transfer, call, instantiate

These tests verify that those functions return the error types
which are declared in its docs.

* Make it more pronounced that to_execution_result handles trap_reason

* Improve ReturnCode docs

* Fix whitespace issues in wat files

* Improve ReturnCode doc

* Improve ErrorOrigin doc and variant naming

* Improve docs on ExecResult and ExecError

* Encode u32 sentinel value as hex

* with_nested_context no longer accepts an Option for trie

* Fix successful typo

* Rename InvalidContractCalled to NotCallable

substrate/frame/contracts/src/lib.rs

@@ -95,6 +95,7 @@ use crate::wasm::{WasmLoader, WasmVm};
 
 pub use crate::gas::{Gas, GasMeter};
 pub use crate::exec::{ExecResult, ExecReturnValue};
+pub use crate::wasm::ReturnCode as RuntimeReturnCode;
 
 #[cfg(feature = "std")]
 use serde::{Serialize, Deserialize};
@@ -420,9 +421,30 @@ decl_error! {
 		/// the subsistence threshold. No transfer is allowed to do this in order to allow
 		/// for a tombstone to be created. Use `ext_terminate` to remove a contract without
 		/// leaving a tombstone behind.
-		InsufficientBalance,
+		BelowSubsistenceThreshold,
+		/// The newly created contract is below the subsistence threshold after executing
+		/// its contructor. No contracts are allowed to exist below that threshold.
+		NewContractNotFunded,
+		/// Performing the requested transfer failed for a reason originating in the
+		/// chosen currency implementation of the runtime. Most probably the balance is
+		/// too low or locks are placed on it.
+		TransferFailed,
+		/// Performing a call was denied because the calling depth reached the limit
+		/// of what is specified in the schedule.
+		MaxCallDepthReached,
+		/// The contract that was called is either no contract at all (a plain account)
+		/// or is a tombstone.
+		NotCallable,
 		/// The code supplied to `put_code` exceeds the limit specified in the current schedule.
 		CodeTooLarge,
+		/// No code could be found at the supplied code hash.
+		CodeNotFound,
+		/// A buffer outside of sandbox memory was passed to a contract API function.
+		OutOfBounds,
+		/// Input passed to a contract API function failed to decode as expected type.
+		DecodingFailed,
+		/// Contract trapped during execution.
+		ContractTrapped,
 	}
 }