Problem: E95 is possible if a buffer called "[Command Line]" already
exists when opening the cmdwin. This can also happen if the
cmdwin's buffer could not be deleted when closing.
Solution: Un-name the cmdwin buffer, and give it a special name instead,
similar to what's done for quickfix buffers and for unnamed
prompt and scratch buffers. As a result, BufFilePre/Post are
no longer fired when opening the cmdwin. Add a "command" key
to the dictionary returned by getbufinfo() to differentiate
the cmdwin buffer instead. (Sean Dewar)
Cherry-pick test_normal changes from v9.0.0954.
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