[AMH] Xtokens add MigrationPhase

[zjb0807]

paritytech/polkadot-sdk#9054 (comment)

instead of AcalaNetwork/Acala#2915

Add MigrationPhase

pub enum MigrationPhase {
	/// Not started
	#[default]
	NotStarted,
	/// Started
	InProgress,
	/// Completed
	Completed,
}

• MigrationStatus default status is NotStarted, chain_part returns Location::parent().
• When AHM migration starts, need to change MigrationStatus to InProgress with MigrationPhaseUpdateOrigin, chain_part returns None to disable reserve asset.
• When AHM migration finishes, need to change MigrationStatus to Completed with MigrationPhaseUpdateOrigin, chain_part returns Location::new(1, [Parachain(ASSET_HUB_ID)])

[codecov]

Codecov Report

❌ Patch coverage is 91.42857% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.97%. Comparing base (c02a0ba) to head (c0d8a10).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
xtokens/src/lib.rs	91.42%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1033      +/-   ##
==========================================
- Coverage   66.02%   65.97%   -0.06%     
==========================================
  Files          48       48              
  Lines        3688     3697       +9     
==========================================
+ Hits         2435     2439       +4     
- Misses       1253     1258       +5     

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