light-client-wasm: provide basic database API for JS

[Officeyutong]

Provide some basic database API to query database usage, currently there is only one API:

• LightClient.getStoreRecordCount(): Returns how many records are in the light client store

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.80%. Comparing base (cc8f4ab) to head (6a64650).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #231   +/-   ##
========================================
  Coverage    71.80%   71.80%           
========================================
  Files           27       27           
  Lines         6942     6942           
========================================
  Hits          4985     4985           
  Misses        1957     1957           

Flag	Coverage Δ
unittests	71.80% <ø> (ø)

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