feat(core): allow to pause/resume query result observers

[sranka]

This PR allows pausing query results by returning false in the next callback of queryApi.queryLines and queryApi.queryRows consumer. The consumer must define useResume callback that receives a function that resumes receiving data when called. This feature adds a low-level (node.js stream) style of lossless backpressure to query result processing via communication observer.

Method signatures changed, the next callback of CommunicationObserver and FluxResultObserver can newly return also a boolean value, false value will stop processing. All these changes are backward compatible, no change is required for the existing code.

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• A test has been added if appropriate
• yarn test completes successfully
• Commit messages are conventional

[codecov-commenter]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage 👍

Coverage data is based on head (ba10b46) compared to base (bb3a52b).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #588   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           33        33           
  Lines         1273      1333   +60     
  Branches       306       323   +17     
=========================================
+ Hits          1273      1333   +60     

Impacted Files	Coverage Δ
packages/core/src/impl/browser/FetchTransport.ts	100.00% <100.00%> (ø)
...ges/core/src/impl/completeCommunicationObserver.ts	100.00% <100.00%> (ø)
packages/core/src/impl/node/NodeHttpTransport.ts	100.00% <100.00%> (ø)
packages/core/src/results/chunksToLines.ts	100.00% <100.00%> (ø)
packages/core/src/results/linesToTables.ts	100.00% <100.00%> (ø)

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[bednar]

LGTM 👍

What do you think about add new example which with pause/resume behaviour?

[sranka]

LGTM +1

What do you think about add new example which with pause/resume behaviour?

The ultimate goal is to switch to reading query results from an async iterable (in a simple for await loop), I am working on it now. All the query examples and demos will be changed to show primarily async iterables, the existing observable consumption of results will not be then a preferred result consumption method. Therefore I think that it can live without an example.