rpc: add decimals/name/symbol data to getNEPXXBalance

[roman-khimov]

See neo-project/neo-modules#738 and neo-project/neo-modules#741.

[codecov]

Codecov Report

Merging #2581 (c356c14) into master (039fcda) will increase coverage by 0.03%.
The diff coverage is 52.11%.

@@            Coverage Diff             @@
##           master    #2581      +/-   ##
==========================================
+ Coverage   84.89%   84.93%   +0.03%     
==========================================
  Files         297      297              
  Lines       37259    37304      +45     
==========================================
+ Hits        31632    31683      +51     
+ Misses       4278     4260      -18     
- Partials     1349     1361      +12     

Impacted Files	Coverage Δ
pkg/network/server_config.go	100.00% <ø> (ø)
pkg/rpc/server/server.go	76.28% <52.11%> (-1.06%)	⬇️
cli/smartcontract/smart_contract.go	92.17% <0.00%> (-0.37%)	⬇️
pkg/core/native/management.go	92.39% <0.00%> (+0.01%)	⬆️
pkg/network/message.go	96.26% <0.00%> (+0.74%)	⬆️
pkg/services/oracle/request.go	63.01% <0.00%> (+5.02%)	⬆️
pkg/network/message_string.go	83.87% <0.00%> (+6.45%)	⬆️
pkg/core/transaction/signer.go	87.50% <0.00%> (+12.50%)	⬆️
pkg/services/oracle/oracle.go	88.37% <0.00%> (+15.50%)	⬆️

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