vm: make EQUAL type strict

[fyrchik]

Do not perform type conversions when comparing elements.
Close #1211 .

[codecov]

Codecov Report

Merging #1225 into master will decrease coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1225      +/-   ##
==========================================
- Coverage   66.79%   66.76%   -0.04%     
==========================================
  Files         199      199              
  Lines       17011    17005       -6     
==========================================
- Hits        11363    11353      -10     
- Misses       5034     5038       +4     
  Partials      614      614              

Impacted Files	Coverage Δ
pkg/vm/stackitem/item.go	90.04% <100.00%> (-0.56%)	⬇️
pkg/rpc/client/wsclient.go	83.22% <0.00%> (-1.35%)	⬇️

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