Support filter_map on collect_iterator in wasm db implementation

[Officeyutong]

This PR updated light-client-wasm and light-client-wasm-db-* to make collect_iterator supports filter_map, which can be used to filter result by keys.

After this PR, argument limit of get_cells, get_transactions will work properly.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.80%. Comparing base (d5dd7c1) to head (ccbc2bd).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #238   +/-   ##
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  Coverage    71.80%   71.80%           
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  Files           27       27           
  Lines         6942     6942           
========================================
  Hits          4985     4985           
  Misses        1957     1957           

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

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