Code inspection should render providers' results independently one from another

[busykai]

Current implementation of Code Inspection waits for all linters to finish before rendering the results in the problems panel. It may become significantly noticeable with the introduction of asynchronous linters which may use a network service or significant amount of time to prepare for the first run. "Fast" linters which provide results quickly should not be dependent on long-running provider to deliver the results. At the same time, on the other hand, should not be discriminating long-running providers, hence the timeout mechanism which #6530 introduces should be replaced with by decoupling providers' execution and render the result immediately once a provider delivers them.