xcm-emulator

[NachoPal]

Improve xcm-emulator, in order of priority:

• [xcm-emulator] Decouple the AccountId type from AccountId32 polkadot-sdk#1381
• [xcm-emulator] Add on_initialize and on_finalize hooks polkadot-sdk#1384
• [xcm-emulator] Restructure Parachains Integration Tests polkadot-sdk#1389
• [xcm-emulator] Allow Chains and Network imports from integration-tests-common crate polkadot-sdk#1383
• [xcm-emulator] Add Documentation and examples polkadot-sdk#1385
• [xcm-emulator] Parachain's block execution should process only its messages polkadot-sdk#1388
• assert_expected_events! gives false positives on inner enum values  polkadot-sdk#2460