refactor fungibles impl

[wangjj9219]

No description provided.

[codecov-commenter]

Codecov Report

Merging #923 (e9b684d) into master (f7c8b38) will increase coverage by 0.22%.
Report is 2 commits behind head on master.
The diff coverage is 78.07%.

@@            Coverage Diff             @@
##           master     #923      +/-   ##
==========================================
+ Coverage   78.40%   78.63%   +0.22%     
==========================================
  Files         105      108       +3     
  Lines       10782    11387     +605     
==========================================
+ Hits         8454     8954     +500     
- Misses       2328     2433     +105     

Files Changed	Coverage Δ
asset-registry/src/mock/para.rs	70.73% <ø> (ø)
currencies/src/lib.rs	48.36% <ø> (ø)
currencies/src/mock.rs	94.11% <ø> (ø)
payments/src/mock.rs	95.65% <ø> (ø)
traits/src/currency.rs	39.58% <0.00%> (ø)
xtokens/src/mock/para.rs	59.09% <ø> (ø)
xtokens/src/mock/para_relative_view.rs	24.39% <ø> (ø)
xtokens/src/mock/para_teleport.rs	15.78% <ø> (ø)
tokens/src/impls.rs	37.16% <41.76%> (+11.07%)	⬆️
tokens/src/impl_currency.rs	68.90% <68.90%> (ø)
... and 10 more

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[wangjj9219]

need to override the default impl of Unbalanced::increase_balance to support DustRemovalWhitelist, currently blocked by paritytech/substrate#14388

[xlc]

should try to integrate with those tests paritytech/substrate#13852