Add listen for Writer and WriterT

[jooohn]

#2304

I'm sorry if someone is already working on this issue, but since there's no action for a month, I just wrote listen for Writer and WriterT.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@207bb0d). Click here to learn what that means.
The diff coverage is 50%.

@@            Coverage Diff            @@
##             master    #2916   +/-   ##
=========================================
  Coverage          ?   94.23%           
=========================================
  Files             ?      364           
  Lines             ?     6956           
  Branches          ?      201           
=========================================
  Hits              ?     6555           
  Misses            ?      401           
  Partials          ?        0

Impacted Files	Coverage Δ
core/src/main/scala/cats/data/package.scala	80% <0%> (ø)
core/src/main/scala/cats/data/WriterT.scala	91.33% <66.66%> (ø)

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