sibling token rework

[zqhxuyuan]

relates to: #1773

the asset-registry module could used for not only statemine/statemint assets, but also sibling token(i.e BNC, PHA etc). thus for new sibling token onboard to acala, now we can use register_foreign_asset dispatch call of asset-registry instead of merge PR to acala code base from parachain team.

a side-effect is asset-registry use foreign-asset-id which is number instead of TokenSymbol enum, thus in front/dapp we may need TokenSymbol mapping to foreign-asset-id, make sure the token mapping is correct.

todo list:

• Trader bunch of FixedRateOfFungible
• migrations

[codecov]

Codecov Report

Merging #1785 (dd3c441) into master (8bd22c5) will decrease coverage by 0.64%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1785      +/-   ##
==========================================
- Coverage   85.81%   85.17%   -0.65%     
==========================================
  Files          78       74       -4     
  Lines       17388    15922    -1466     
==========================================
- Hits        14921    13561    -1360     
+ Misses       2467     2361     -106     

Impacted Files	Coverage Δ
modules/asset-registry/src/lib.rs	59.78% <100.00%> (ø)
modules/currencies/src/lib.rs
modules/nft/src/lib.rs
modules/nft/src/tests.rs
modules/currencies/src/tests.rs

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 8bd22c5...dd3c441. Read the comment docs.

[xlc]

This will break compatibility for both SDK and existing runtime storages (e.g. BNC swap pair)
It should be possible to do some migration but it isn't that much beneficial to migrate.