Contracts: xcm host fn fixes (#3086)

## Xcm changes:
- Fix `pallet_xcm::execute`, move the logic into The `ExecuteController`
so it can be shared with anything that implement that trait.
- Make `ExecuteController::execute` retursn `DispatchErrorWithPostInfo`
instead of `DispatchError`, so that we don't charge the full
`max_weight` provided if the execution is incomplete (useful for
force_batch or contracts calls)
- Fix docstring for `pallet_xcm::execute`, to reflect the changes from
#2405
- Update the signature for `ExecuteController::execute`, we don't need
to return the `Outcome` anymore since we only care about
`Outcome::Complete`

## Contracts changes:

- Update host fn `xcm_exexute`, we don't need to write the `Outcome` to
the sandbox memory anymore. This was also not charged as well before so
it if fixes this too.
- One of the issue was that the dry_run of a contract that call
`xcm_execute` would exhaust the `gas_limit`.

This is because `XcmExecuteController::execute` takes a `max_weight`
argument, and since we don't want the user to specify it manually we
were passing everything left by pre-charghing
`ctx.ext.gas_meter().gas_left()`

- To fix it I added a `fn influence_lowest_limit` on the `Token` trait
and make it return false for `RuntimeCost::XcmExecute`.
- Got rid of the `RuntimeToken` indirection, we can just use
`RuntimeCost` directly.

---------

Co-authored-by: command-bot <>

polkadot/xcm/xcm-builder/src/controller.rs

@@ -18,7 +18,10 @@
 //! Controller traits defined in this module are high-level traits that will rely on other traits
 //! from `xcm-executor` to perform their tasks.
 
-use frame_support::pallet_prelude::DispatchError;
+use frame_support::{
+	dispatch::{DispatchErrorWithPostInfo, WithPostDispatchInfo},
+	pallet_prelude::DispatchError,
+};
 use sp_std::boxed::Box;
 use xcm::prelude::*;
 pub use xcm_executor::traits::QueryHandler;
@@ -52,7 +55,8 @@ pub trait ExecuteController<Origin, RuntimeCall> {
 	/// Weight information for ExecuteController functions.
 	type WeightInfo: ExecuteControllerWeightInfo;
 
-	/// Attempt to execute an XCM locally, and return the outcome.
+	/// Attempt to execute an XCM locally, returns Ok with the weight consumed if the execution
+	/// complete successfully, Err otherwise.
 	///
 	/// # Parameters
 	///
@@ -63,7 +67,7 @@ pub trait ExecuteController<Origin, RuntimeCall> {
 		origin: Origin,
 		message: Box<VersionedXcm<RuntimeCall>>,
 		max_weight: Weight,
-	) -> Result<Outcome, DispatchError>;
+	) -> Result<Weight, DispatchErrorWithPostInfo>;
 }
 
 /// Weight functions needed for [`SendController`].
@@ -137,8 +141,9 @@ impl<Origin, RuntimeCall> ExecuteController<Origin, RuntimeCall> for () {
 		_origin: Origin,
 		_message: Box<VersionedXcm<RuntimeCall>>,
 		_max_weight: Weight,
-	) -> Result<Outcome, DispatchError> {
-		Ok(Outcome::Error { error: XcmError::Unimplemented })
+	) -> Result<Weight, DispatchErrorWithPostInfo> {
+		Err(DispatchError::Other("ExecuteController::execute not implemented")
+			.with_weight(Weight::zero()))
 	}
 }