[trie] Add sortIfNeed() in sortedlist

[Liuhaai]

Most trie operations are getState(), which load branchnode from hashnode and call Search(). Therefore, the trie performance improves by avoiding sorting work when loading branchnode

[codecov]

Codecov Report

Merging #3172 (3f795a8) into master (56801c5) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3172      +/-   ##
==========================================
- Coverage   75.13%   75.13%   -0.01%     
==========================================
  Files         221      221              
  Lines       21013    21021       +8     
==========================================
+ Hits        15789    15795       +6     
- Misses       4388     4389       +1     
- Partials      836      837       +1     

Impacted Files	Coverage Δ
db/trie/mptrie/sortedlist.go	100.00% <100.00%> (ø)
db/trie/mptrie/extensionnode.go	91.22% <0.00%> (-1.76%)	⬇️

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[CoderZhi]

what if a new created sortedlist is iterated?

[Liuhaai]

what if a new created sortedlist is iterated?

The internal list should be accessed via sl.List(), like for _, idx := range b.indices.List() {}