Channel-postmessage: handle events from the same window

[Hypnosphi]

Issue: #1407 was intended to add an ability to use channel as an event bus working regardless of whether events comes to the same or to another (preview vs manager) window. But right now it works only with channel-websocket. This PR adds this ability to channel-postmessage as well

[codecov]

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@@           Coverage Diff            @@
##             master   #3519   +/-   ##
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  Coverage          ?   92.5%           
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  Files             ?       6           
  Lines             ?      40           
  Branches          ?       2           
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  Hits              ?      37           
  Misses            ?       2           
  Partials          ?       1

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