[pallet-xcm] Adjust benchmarks (teleport_assets/reserve_transfer_assets) not relying on ED (#3464)

## Problem
During the bumping of the `polkadot-fellows` repository to
`polkadot-sdk@1.6.0`, I encountered a situation where the benchmarks
`teleport_assets` and `reserve_transfer_assets` in AssetHubKusama
started to fail. This issue arose due to a decreased ED balance for
AssetHubs introduced
[here](https://github.com/polkadot-fellows/runtimes/pull/158/files#diff-80668ff8e793b64f36a9a3ec512df5cbca4ad448c157a5d81abda1b15f35f1daR213),
and also because of a [missing CI
pipeline](https://github.com/polkadot-fellows/runtimes/issues/197) to
check the benchmarks, which went unnoticed.

These benchmarks expect the `caller` to have enough:
1. balance to transfer (BTT)
2. balance for paying delivery (BFPD).
 
So the initial balance was calculated as `ED * 100`, which seems
reasonable:
```
const ED_MULTIPLIER: u32 = 100;
let balance = existential_deposit.saturating_mul(ED_MULTIPLIER.into());`
```
The problem arises when the price for delivery is 100 times higher than
the existential deposit. In other words, when `ED * 100` does not cover
`BTT` + `BFPD`.

I check AHR/AHW/AHK/AHP and this problem has only AssetHubKusama
```
ED: 3333333
calculated price to parent delivery:  1031666634  (from xcm logs from the benchmark)
---

3333333 * 100 - BTT(3333333) - BFPD(1031666634) = −701666667
```
which results in the error;
```
2024-02-23 09:19:42 Unable to charge fee with error Module(ModuleError { index: 31, error: [17, 0, 0, 0], message: Some("FeesNotMet") })
Error: Input("Benchmark pallet_xcm::reserve_transfer_assets failed: FeesNotMet")
     
```

## Solution

The benchmarks `teleport_assets` and `reserve_transfer_assets` were
fixed by removing `ED * 100` and replacing it with `DeliveryHelper`
logic, which calculates the (almost real) price for delivery and sets it
along with the existential deposit as the initial balance for the
account used in the benchmark.


## TODO

- [ ] patch for 1.6 -
https://github.com/paritytech/polkadot-sdk/pull/3466
- [ ] patch for 1.7 -
https://github.com/paritytech/polkadot-sdk/pull/3465
- [ ] patch for 1.8 - TODO: PR

---------

Co-authored-by: Francisco Aguirre <franciscoaguirreperez@gmail.com>

cumulus/parachains/runtimes/collectives/collectives-westend/src/lib.rs

@@ -986,8 +986,21 @@ impl_runtime_apis! {
 			use cumulus_pallet_session_benchmarking::Pallet as SessionBench;
 			impl cumulus_pallet_session_benchmarking::Config for Runtime {}
 
+			parameter_types! {
+				pub ExistentialDepositAsset: Option<Asset> = Some((
+					xcm_config::WndLocation::get(),
+					ExistentialDeposit::get()
+				).into());
+			}
+
 			use pallet_xcm::benchmarking::Pallet as PalletXcmExtrinsicsBenchmark;
 			impl pallet_xcm::benchmarking::Config for Runtime {
+				type DeliveryHelper = cumulus_primitives_utility::ToParentDeliveryHelper<
+					xcm_config::XcmConfig,
+					ExistentialDepositAsset,
+					xcm_config::PriceForParentDelivery,
+				>;
+
 				fn reachable_dest() -> Option<Location> {
 					Some(Parent.into())
 				}
@@ -996,7 +1009,7 @@ impl_runtime_apis! {
 					// Relay/native token can be teleported between Collectives and Relay.
 					Some((
 						Asset {
-							fun: Fungible(EXISTENTIAL_DEPOSIT),
+							fun: Fungible(ExistentialDeposit::get()),
 							id: AssetId(Parent.into())
 						}.into(),
 						Parent.into(),